Background: Medical students present higher numbers of physician relatives than expectable from the total population prevalence of physicians. Evidence for such a familial aggregation effect of physicians has emerged in investigations from the Anglo-American, Scandinavian, and German-speaking areas. In particular, past data from Austria suggest a familial aggregation of the medical, as well as of the psychological and psychotherapeutic, professions among medical and psychology undergraduates alike. Here, we extend prior related studies by examining (1) the extent to which familial aggregation effects apply to the whole nation-wide student census of all relevant (eight) public universities in Austria; (2) whether effects are comparable for medical and psychology students; (3) and whether these effects generalize to relatives of three interrelated health professions (medicine, psychology, and psychotherapy). Methods: We investigated the familial aggregation of physicians, psychologists, and psychotherapists, based on an entire cohort census of first-year medical and psychology students (n = 881 and 920) in Austria with generalized linear mixed models. Results: For both disciplines, we found strong familial aggregation of physicians, psychologists, and psychotherapists. As compared with previous results, directionally opposite time trends within disciplines emerged: familial aggregation of physicians among medical students has decreased, whilst familial aggregation of psychologists among psychology students has increased. Further, there were sex-of-relative effects (i.e., more male than female physician relatives), but no substantial sex-of-student effects (i.e., male and female students overall reported similar numbers of relatives for all three professions of interest). In addition, there were age-benefit effects, i.e., students with a relative in the medical or the psychotherapeutic profession were younger than students without, thus suggesting earlier career decisions. Conclusions: The familial aggregation of physicians, psychologists, and psychotherapists is high among medical and psychology undergraduates in Austria. Discussed are implications of these findings (e.g., gender equity, feminization of the medical field, ideas for curricular implementation and student counselling), study limitations, and avenues for future research.