Osteomyelitis in the adult is a rare disease. In this review we present the diagnostic and therapeutic principles for treatment of chronic osteomyelitis of long bones in adults. The most important step in treating osteomyelitis is the detection of the offending bacteria. The diagnostics should be performed with tissue and fluids from the depth of the wound. Superficial samples and swaps from fistulas should not be used to determine the offending bacteria. The defining criteria of chronic osteomyelitis are necrotic and non vascularized bony tissue. The appropriate therapy includes radical excision of the diseased bone and infected scar tissue, closure of the wound with well vascularized tissue including (muscle) flaps, stabilization of instable situations by external fixation and administration of adequate antibiotics. Remaining necrotic bone tissue is one of the most relevant sources for recurrent infection.