The authors report a case of idiopathic priapism in a 4 year old boy. This is an exceptional disease at this age, which was treated urgently by creating a cavernosospongiosum fistula with a rapidly favourable clinical course. The prognosis appears to be related to the rapidity of treatment. Although aetiological treatment can be proposed in the case of priapism due to haematological malignancies, only surgical treatment appears to be truly effective in the other forms.