OBJECTIVES: The diagnosis of hypogonadism is established in symptomatic men with consistently low levels of serum testosterone, whether due to specific diagnoses, such as Klinefelter syndrome, or non-specific diagnoses, which often occur with aging. Testosterone gels are the most common form of testosterone replacement therapy for hypogonadism in the United States, but little is known about patient adherence and persistence with therapy. This study seeks to examine testosterone gel adherence and persistence among hypogonadism patients.      METHODS: The type of hypogonadism (specific versus non-specific) was classified using either ICD-9-CM diagnostic codes or testosterone prescription codes in the Thomson Reuters MarketScan® Database in 2009. Medication persistence was defined as the length of therapy (LOT) from the index date to the earliest ending date of the last prescription, defined as either the date of the first gap of >30 days between prescriptions or the end of study period (12 months). Medication adherence was measured by medication possession ratio (MPR) in the 6 months follow-up period. Adherence rate was defined as percent of MPR ≥0.8.  LOT, MPR and adherence rate were calculated by diagnostic code and age group and compared using t-test or chi-square test. RESULTS: 91,200 men met study criteria for hypogonadism: 11.1% with specific and 89.9% with non-specific diagnostic codes.  The mean LOT was 196 days and 178 days, respectively (p<0.0001). MPR and adherence rates were similar between men with specific (0.4 and 8.6%, respectively) and non-specific (0.4 and 9.0%, respectively) diagnoses. LOT, MPR and adherence rate were numerically similar across all age groups. CONCLUSIONS: Unexpectedly, diagnostic specificity and age were not found to be key etiologic factors in testosterone gel adherence and persistence for hypogonadal men. Unexplored factors that might provide more sensitivity include other testosterone application methods, hypogonadal symptom severity, and ascertainment of testosterone levels.