Testicular or scrotal involvement has been reported in children with Henoch-Schonlein purpura (HSP), but there are very few reports on penile involvement. We report the initial and follow-up ultrasonographic findings of scrotal and penile involvement of HSP in a 5-year-old boy. On ultrasonography, scrotal soft tissue thickening and epididymal swelling with increased vascularity were noted, and on the penis, a focal mass-like lesion appeared on the dorsal surface of the distal penis, having a hypoechoic mass-like appearance without visible vascular flow on a Doppler study. After 2 days of treatment, follow-up ultrasonography showed normal scrotum and penis with a resolved soft tissue mass-like lesion. Therefore, we think that HSP ultrasonographic findings involving the scrotum and penis might help to diagnose scrotal and penile involvement in a case of HSP and to avoid unnecessary medication and/or surgical procedures.