We report the case of a 32-year-old woman who had pruritic urticarial skin lesions associated with episodes of arthralgia. The first site affected by the eruption was the inside surface of the thighs; the patient also reported the presence of leukorrhea. The woman had previously been treated with H1 antagonist with moderate and transitory results; skin lesions reappeared just after the interruption of the treatment. Her biochemical data showed increased levels of erythrocyte sedimentation rate, blood eosinophilia and hypocomplementemia. Antinuclear antibodies, rheumatoid factor, cryoglobulins and serological diagnosis for hepatitis or mononucleosis viruses resulted negative. Considering the initial site of the cutaneous features and the presence of leukorrhea, we requested a vaginal smear and a culture of the cervical secretion, which revealed the presence of a Trichomonas infection. Furthermore, the SDS-PAGE revealed the presence of a molecular mass of 230,000 Da (230-kDa) in the serum, which indicated a Trichomonas surface protein. The following treatment with oral metronidazole caused the eradication of the Trichomonas infection after 3 weeks and subsequently the resolution of the urticarial clinical features. We wish to underline that in the presence of a case of urticaria vasculitis syndrome which seems to be without cause, it is important to investigate every diagnostic suspicion scrupulously.