Reported here is the case of a 29-year-old male with cervical lymphadenopathy, fever and weight loss, followed by acute painful osteomyelitis of the left hip joint due to cat-scratch disease. The diagnosis was established by detection of IgG antibodies to Bartonella henselae in serum and histologic examination of a lymph node including a positive polymerase chain reaction test. Treatment consisted of clarithromycin and cefotiam for 2 weeks. Four weeks after discharge, all of the patient's symptoms had completely resolved. Magnetic resonance imaging of the left hip joint showed marked regression of bone inflammation 4 months later and normalization after 8 months. Cat-scratch disease should be considered in the differential diagnosis of osteomyelitis in an adult, especially when lymphadenitis is present.