OBJECTIVE: To present a case which demonstrates the unusual clinical features of secondary syphilis that may be encountered in tropical Australia. CLINICAL FEATURES: A syphilitic aetiology was initially missed in a Caucasian female presenting with a rare form of syphilis, "lues maligna", characterised by nodulo-ulcerative skin lesions, fever, meningism and a relapsing course. CONCLUSION: Secondary syphilis is usually manifest in the Northern Territory by a characteristic palmo-plantar psoriasiform eruption with variable involvement of skin in other body areas. The disease is most commonly seen in the young adult Aboriginal population. However, atypical presentations can occur and vigilance must be maintained for a syphilitic aetiology in unusual skin lesions. The disease may produce significant individual morbidity and may be transmitted non-venereally to close contacts in the secondary stage. Genital lesions facilitate the transmission of HIV, making early diagnosis and treatment even more important.