Plasmodium vivax infections caused by strains with low sensitivity to primaquine are widespread in the Western Pacific and Southeast Asia, and have been recently reported from Central America as well. We report a case of primaquine failure in a P. vivax infection acquired in Guatemala. A 28-year-old Italian woman developed two months after returning from Guatemala a vivax malaria attack that was treated with a standard chloroquine course (1,500 mg over three days) combined with primaquine (15 mg/day for 14 days). Two months later, she had a relapse that was again treated with chloroquine and primaquine at the same doses. After two more months, a second relapse occurred: this time primaquine (30 mg/day for 14 days was administered; the patient remained well during a follow-up period of six months and all parasitologic examination results were negative. Doses of primaquine as high as 6 mg/kg total dose may be indicated in the treatment of vivax malaria cases from Central America.