Abstract: In this study shorter duration of antirelapse therapy was compared to that of 8 weeks regimen. In 1998 and 1999 antirelapse therapy of vivax in Sistan and Baluchestan province in southeast of Iran was done with different regimens according to manpower and executive facilities. A cohort study was compared clinically and parasitological relapse of vivax malaria in 200 patients with one-week therapy, 200 patients with 2 weeks, 800 patients with 4 weeks and 500 patients with 8 weeks therapy by primaquine. Relapse rates of vivax malaria by each regimen were 23.8, 13.2, 5.4 and 4.6%, respectively. Relative risk of relapse in comparison with 8 weeks regimen was 5.2, 2.9 and 1.2, respectively. Number Need to Harm (NNH) was 5, 12 and 125. Interval of the first relapse varied between 6 to 52 weeks with the mean of 28.8 weeks (CI 95%: 24.2-33.1). The relapse rate was not different between men and women. The relapse rate by 4 and 8 weeks regimes were low and there was not significant difference of relapse rate in 4 and 8 weeks regimes. It is recommended to use 4 weeks therapy instead of 8 weeks therapy in special situations.