Three cases of spontaneous, partial, unilateral thrombosis of the corpus cavernosum are described. The patients presented with a painful mass in the perineum without priapism. Diagnosis was made through ultrasound evaluation and magnetic resonance imaging, showing unilateral, partial thrombosis of the corpus cavernosum. Treatment consisted of systemic anticoagulation. In all three cases, the thrombosis resolved spontaneously over several months without complications. The aetiology of partial thrombosis of the corpus cavernosum remains unclear, but conservative management of this rare condition appears to be effective and safe.