In 1873, Sigmund Freud graduated from the Sperl Gymnasium and was faced with the question of what to study at the University of Vienna. There was never a question about whether or not he would go to the university; he had long been on a path toward a professional life in academics, medicine or law. It was now simply a matter of deciding which path to take. Despite initially leaning toward law, partly on the basis of a friend's recommendation, Freud eventually decided on medicine. It was not that he was eager to be a physician: in fact, although he eventually took great satisfaction in his therapeutic work, Freud never felt at home in the medical profession. Freud's true passion was science.

Freud started medical school at seventeen, an unusually early age. It took him an unusually long time to finish medical school. Not until 1881 did he finally received his medical degree. Reports from friends who knew him during that time, as well as information from Freud's own letters, suggest that Freud was less diligent about his medical studies than he might have been. He focused instead on scientific research. He started by studying the sexual organs of eels–an odd and amusing foreshadowing of the psychoanalytic theories that would follow more than twenty years later. According to all reports, Freud performed his assigned task satisfactorily, but without brilliant results. In 1877, disappointed at his results and perhaps less than thrilled at the prospect of dissecting more eels, Freud moved to the laboratory of Ernst Brücke, the man who was to become his first and most important role model in science.

Brücke was a physiologist from the strictly physicalist school that had first arisen with Freud's father's generation. Brücke and others argued that special "vital" forces were not necessary to explain life; rather, all biological phenomena could be explained by reference to basic physical laws, even if–as was certainly the case in Brücke's and Freud's time–the connection to those laws was not apparent. As a physiologist, Brücke was concerned with the function of particular cells and organs, not just with their structure. Brücke's work thus focused on the attempt to discover basic physical laws that governed the processes that took place in living systems.

When Freud formulated his theories of psychoanalysis in the 1890s, he abandoned the physicalism of Brücke's position, but retained the search for universal laws and the emphasis on processes, or dynamics. ("Psychodynamic psychology" is a modern term that refers to Freud's theories of psychology and others like it that describe the mind in terms of dynamic interactions between different mental structures.) Freud's later focus on the sex drive can be seen, in two ways, as a result of his study under Brücke. First, the focus was a nod to physicalism–an attempt to link the vicissitudes of the mind to changes in the body (i.e. sexual arousal). Second, it was a strongly reductionistic approach–an attempt to boil down the huge complexity of human motivation into one basic drive.

In Brücke's laboratory, Freud worked on brain anatomy and histology. His most important project was determining whether a certain kind of nerve cell in frogs was the same kind found in humans, or whether there were essential differences between the nerve cells of humans and "lower" animals. This project had relevance to an ongoing debate that had been sparked by Charles Darwin's Origin of the Species, published some twenty years earlier: is humanity above the laws of nature, or subject to them like any other living organism? Freud's work in Brücke's lab showed that the human and frog spinal neurons cells were of the same type. In a small way, Freud thus contributed to Darwin's quest to show that humans were genetically and historically linked to all other animals on earth. Later, Freud would claim that his own discovery– psychoanalysis–was the next step after Darwin's in bringing humanity down from its pedestal.

Early in Freud's university career, in 1875, he took his first trip to England. There, he visited his half-brother Emmanuel and his family in Manchester. Freud adored the English language and culture, and greatly enjoyed his first visit. He returned only twice in his life, once in 1908 to visit his brother in Manchester again, and again in 1938, sixty-three years after his first visit, when the Nazi takeover of Austria finally forced him to flee Vienna.

In 1881, Freud made the acquaintance of Martha Bernays, the sister of one of Freud's university friends. It seems to have been love at first sight. Freud and Martha were both far too poor to marry, but nonetheless they secretly got engaged. Because of Freud's meager income, they would not be able to marry for another five years. Martha spent most of their engagement in Hamburg, far from her fiancé. They got on well despite their distance, for Freud proved to be a diligent and heartfelt, though sometimes overbearing, correspondent.