Simple SummaryObstructive sleep apnea (OSA) increases the risk of numerous cancers. Nevertheless, testicular cancer prevalence in OSA patients has not been documented. Based on KNHIS data, this study examines OSA’s effect on testicular cancer incidence. A total of 152,801 newly diagnosed male adult OSA patients and 764,005 controls were studied. Even after confounding correction, OSA’s HR for testicular cancer was 1.58 (95% CI: 0.92–2.60). The subgroup analysis showed a 3.39 (95% CI: 1.08–10.06) HR for testicular cancer in those over 65. The 20–40 and 40–65 age groups had no significant HR. OSA may not affect testicular cancer in adults in general. However, those over 65 may be more susceptible to OSA-related testicular cancer than younger individuals.AbstractObstructive sleep apnea (OSA) has been linked to an increased risk of acquiring many types of cancer. No data on the prevalence of testicular cancer in OSA patients have been reported in the literature. The goal of the present investigation is to find out the impact of OSA on the incidence of testicular cancer based on the Korea National Health Insurance Service (KNHIS) dataset. A cohort of adult male patients newly registered with OSA in the KNHIS data from 2007 to 2014 who had no history of any previous cancer diagnosis was included. The main outcome measure was newly diagnosed testicular cancer in the National Medical Expenses Support Program. The control group was set at five times larger than the OSA group, and it was matched with age and sex. The cumulative incidence and hazard ratio (HR) for the development of testicular cancer were compared between the OSA and control groups. Further subgroup analysis was conducted in the three different age groups. In the study period, a total of 152,801 male adult patients newly diagnosed with OSA were included, whereas 764,005 individuals were recruited as the control group. The HR of OSA for developing testicular cancer was 1.58 (95% confidence interval [CI]: 0.92–2.60), showing no significant HR regardless of confounding adjustment. However, the subgroup analysis revealed a significantly increased HR to develop testicular cancer of 3.39 (95% CI: 1.08–10.06) in groups aged more than 65, whereas the age ranges of 20–40 and 40–64 showed no significance (1.19 (0.44–2.75) and 1.27 (0.50–2.80), respectively). OSA may not influence the incidence of testicular cancer in the general adult population. However, compared to younger males, males over 65 may be more susceptible to OSA when it comes to developing testicular cancer.