Ulcerative acne was observed in three boys who underwent long-term treatment with high doses of testosterone for excessively tall stature. Even after withdrawal of testosterone therapy, this devastating type of acne still persisted for several months. After starting isotretinoin treatment, two cases progressed to full-blown acne fulminans with systemic manifestations. In these two cases, oral isotretinoin therapy induced multiple lesions of hyperproliferative granulation tissue resembling pyogenic granuloma. Topical steroid treatment proved to be beneficial for this adverse effect. Systemic corticosteroid treatment was administered in one case. High testosterone levels during puberty may be an important trigger mechanism of acne fulminans and may explain why this disease almost exclusively affects male adolescents.