Gnathostomiasis is increasingly reported among travelers returning from endemic areas. Between 2000 and 2004, thirteen patients were diagnosed with imported gnathostomiasis and followed for at least 6 months after treatment. Nine patients presented with cutaneous signs, two with gastrointestinal signs, and two with neurological signs. The median age was 38 years and the female/male sex ratio was 1.6. The patients had visited South East Asia or Central America. The median interval between symptom onset and treatment (with albendazole in 12 cases and ivermectin in one case) was 3.5 months. Post-treatment follow-up lasted a median of 15 months. Eight patients relapsed, a median of 2 months (1-7 months) after initial treatment. These eight patients had a total of 13 relapses, the last occurring a median of 16 months (2-26 months) after initial treatment. Thus patients with imported gnathostomiasis should be monitored for at least 6 months to detect late treatment failure.