Acne fulminans is a rare manifestation that may occur during the evolution of acne vulgaris primarily in male adolescents. Use of isotretinoin, testosterone, and exacerbated immune responses in the body are related triggers. Signs, symptoms and laboratory findings such as fever, hepatomegaly, polyarthralgia, leukocytosis, plaquetose, increased inflammatory markers and transaminases, are characteristic. A bone scan can detect osteolytic lesions in multiple skeletal sites. The treatment is performed with prednisolone, isotretinoin and antibiotics if secondary infection is present. This case describes a male patient with a diagnosis of grade III acne, who developed acne fulminans and bilateral sacroiliitis with inability to ambulate, after initiation of therapy with isotretinoin.