Cellulitis of the penis is an uncommon clinical condition, most often seen in young men, and presents with local and systemic signs that progress rapidly in the absence of treatment. It needs to be differentiated from sexually transmitted infections and dermatological conditions. The present report concerns a case of penile cellulitis in a young, heterosexual man, following sexual intercourse. The clinical presentation, aetiology and management are discussed. Penile swelling in any age group should be viewed with high index of suspicion and sexually transmitted infections should be excluded in young men. Group B haemolytic streptococci are the usual causative organisms, although less virulent organisms should be considered in patients who are immunocompromised. Administration of appropriate antibiotics resolves the local and systemic symptoms and avoids complications.