We conducted one of the first prospective studies to test the hypothesis that the clinical history of priapism underestimates priapism incidence compared to a priapism pain diary. Eligibility criteria were men with SCA between 18-40 years of age who have had at least 3 episodes of priapism in the past 12 months. Seventy-one men with SCA completed the diary for at least 3 months. Due to participant fatigue, only the first three months of the priapism diary were included in the analysis. A total of 298 priapism episodes were recorded, and 80% (57 of 71) of the participants had at least one priapism event. Priapism severity was reported as in the range of moderate to the worst imaginable pain in 81.5% (263 of 298), and the median pain rating was 6 (IQR: 5-8) on a scale from 1 to 10. The monthly incidence rate of priapism per participant based on history versus a self-report pain diary was 2.0 (95% confidence interval 1.9 - 2.1) and 1.4 (95% confidence interval 1.2 - 1.6), respectively (p<0.001). For participants that had a prior priapism episode, 80% had another episode during the three-month interval follow-up. The median time to that second episode was 27.5 days. Major priapism occurred in 9.9% of episodes and was associated with the sum of future priapism events. Men with SCA and at least 3 priapism episodes in the past 12 months are at significant risk for recurrent priapism in the following 3 months.