Syphilitic infection is usually observed in young patients, and the first stage of the disease (primary syphilis) is characterized by painless cutaneous and lymph node lesions. Herein, we describe a 71-year-old Japanese man with primary syphilis that presented as unilateral inguinal lymphadenopathy without skin lesions. Originally, an incarcerated hernia was clinically suspected. The lymph node pathologically showed suppurative lymphadenitis with vague granulomas; immunohistochemistry was highly suggestive of a syphilitic infection. Primary syphilis was confirmed by positive serological tests. Syphilitic infection should be included in the clinicopathological differential diagnoses for patients with inguinal lymphadenopathy, even in elderly patients without skin lesions.