Background: Balanitis is an inflammation of the glans while balanoposthitis involves both the glans and the foreskin and occurs only in uncircumcised males. After Candida infections, aerobic bacteria are the second most common cause of acute infectious balanoposthitis, mainly streptococci groups B and A, and staphylococci, usually Staphylococcus aureus. Its clinical manifestations including diffuse erythema and oedema. Severe balanopreputial oedema with purulent exudate occurs in erosive balanitis. Diabetes is the most common predisposing factor for balanoposthitis and lichen sclerosus has been associated with diabetes. Therefore, it is recommended that patients with severe or recurrent balanoposthitis and patients with lichen sclerosus undergo screening for diabetes. Case Presentation: A 55-year-old man with diabetes underwent circumcision one month ago due to phimosis resulting from lichen sclerosus. The patient presented with a painful, erosive, and exudative plaque on the glans that had been present for 5 days. Abundant growth of Staphylococcus aureus was obtained in the bacterial culture. The fungal culture was negative. The genital lesions healed completely with treatment using oral cloxacillin and topical mupirocin. Conclusions: We present a diabetic male patient with severe, erosive balanitis caused by Staphylococcus aureus following circumcision to treat phimosis secondary to genital lichen sclerosus. We also highlight the association between diabetes and two genital skin conditions, lichen sclerosus and bacterial balanitis.