A 44-year-old man with well-controlled HIV presented with low-grade fever, pharyngitis, frontal headache, abdominal and shin pain, and abnormal liver function tests 8 weeks after switching from zidovudine to abacavir (while continuing nevirapine and lamivudine). An abacavir reaction was the working diagnosis and thus his antiretroviral regimen was returned to the previously tolerated combination and he received 10 days of oral penicillin (500mg twice daily) for presumptive tonsillitis with significant improvement. A whole-body bone scan demonstrated multiple foci of increased patchy osteoblastic activity of the long bones and skull. Six months later during routine screening, a syphilis rapid plasma reagin (RPR) titre of 128 was detected. Retrospective testing on stored samples demonstrated a first positive RPR at the time of symptomatic presentation. He received three injections of 1.8g benzathine penicillin on a weekly basis with a subsequent decrease in RPR titre and normalisation of the bone scan. Although syphilitic osteitis is rare, this case re-emphasises the importance of considering syphilis when HIV-infected patients present with unusual symptoms. The use of bone scan in this setting and treatment options are discussed. ? CSIRO 2013.