STUDY QUESTION: What is the prevalence of malignant testicular germ cell tumors (TGCT) and its precursors, (pre-) germ cell neoplasia in situ (GCNIS), in late teenagers and adults who have androgen insensitivity syndrome (AIS) and the impact of an individual's genetic susceptibility to development of TGCT? SUMMARY ANSWER: No GCNIS or TGCT was diagnosed, but pre-GCNIS was identified in 14 and 10% of complete and partial AIS patients, respectively, and was associated with a higher genetic susceptibility score (GSS), with special attention for KITLG (rs995030) and ATFZIP (rs2900333). WHAT IS KNOWN ALREADY: Many adult women with AIS decline prophylactic gonadectomy, while data regarding the incidence, pathophysiology and outcomes of TGCT in postpubertal individuals with AIS are lacking. The relevance of genetic factors, such as single nucleotide polymorphisms (SNPs), in predisposing AIS individuals to TGCT is unknown. STUDY DESIGN, SIZE, DURATION: This multicenter collaborative study on prophylactically removed gonadal tissue was conducted in a pathology lab specialized in germ cell tumor biology. PARTICIPANTS/MATERIALS, SETTING, METHODS: Material from 52 postpubertal individuals with molecularly confirmed AIS (97 gonadal samples) was included; the median age at surgery was 17.5 (14-54) years. Immunohistochemical studies and high-throughput profiling of 14 TGCT-associated SNPs were performed. The main outcome measures were the prevalence of pre-GCNIS, GCNIS and TGCT, and its correlation with a GSS, developed based on the results of recent genome-wide association studies. MAIN RESULTS AND ROLE OF CHANCE: The earliest recognizable change preceding GCNIS, referred to as pre-GCNIS, was present in 14% of individuals with complete and 10% of those with partial AIS at a median age of 16 years. No GCNIS or invasive TGCT were found. The median GSS was significantly greater for those with, compared to those without, pre-GCNIS (P = 0.01), with an overlap between groups. Our data suggest important roles for risk alleles G at KITLG (rs995030) and C at ATFZIP (rs2900333), among the 14 studied TGCT-associated SNPs. LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: A limited number of cases were included. WIDER IMPLICATIONS OF THE FINDINGS: Our data suggest that the prevalence of pre-GCNIS in individuals with AIS beyond puberty is around 15%. Genetic susceptibility likely contributes to pre-GCNIS development in AIS but factors related to malignant progression remain unclear. Although data in older patients remain scarce, malignant progression appears to be a rare event, although the natural history of the premalignant lesion remains unknown. Therefore, the practice of routine prophylactic gonadectomy in adults with AIS appears questionable and the patient's preference, after having been fully informed, should be decisive in this matter. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by research grants from the Research Foundation Flanders (FWO) (to M.C.), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq G0D6713N) (to B.B.M. and M.C.) and the European Society for Pediatric Endocrinology (ESPE), granted by Novo Nordisk AB (to J.K.). There are no competing interests.