A population-based matched cohort study has shown that men who receive testosterone replacement therapy are at increased risk of developing stones. Data from the Military Health System Data Repository were analysed and overall 26,586 matched pairs were included. In total, 659 men who received testosterone replacement therapy experienced a stone-related event, compared with 482 men who did not have testosterone (P < 0.0001) at 2 years. No significant difference was observed on the basis of secondary polycythemia, an indirect indicator of increased testosterone levels while on treatment. This risk should be considered when prescribing testosterone.