A previously healthy, 54-year-old woman presented with Mycobacterium chelonae soft tissue infection and osteomyelitis of her left lower leg. The infection had started from soft tissue emerging at the medial aspect of the distal femur and had spread through the bone because of delayed diagnosis. The largely indolent, 8-month course to diagnosis was attributable to unremarkable clinical manifestations combined with a low index of suspicion such as immunocompetent patient and/or inadequate finding of acid-fast bacilli in a lesion smear, characteristic histopathological features, and culture techniques. Soft tissue infection and osteomyelitis were successfully treated without surgical intervention and with a 6-month course of chemotherapy.