Objectives The incidence and duration of sick leave were studied among immigrants and the native-born population in Spain. Methods This observational follow-up study included 1427 immigrants and 2793 Spanish natives treated at five primary care centers in Lleida in 2005 and followed for 6 months. The sick leave causes were coded according to the International Classification of Diseases (10th revision). Multivariate Poisson regressions estimated the rate ratio (RR) for sick leave adjusted for age, and linear regressions evaluated the effect of age, gender, and region of origin on the total number of sick-leave days. Results Altogether 19.5% of the natives and 12.7% of the immigrants had at least one sick-leave episode. The incidence of new episodes per 100 person-years was lower for the immigrants than for the natives (32.5 versus 43.3 for the men and 18.6 versus 35.6 for the women, respectively). The mean duration of sick leave in the 6- month period was 19.4 (SD 29.4) days for the immigrants and 33.5 (SD 39.2) days for the natives. For the men, the risk of sick leave was greater for the natives than for the immigrants (adjusted RR 1.70, 95% confidence interval 1.43–2.02). After adjustment for age, the duration of sick leave for the native workers was 1.5 times greater than for the immigrants. Conclusions Even though sick leave was less frequent among the immigrants than among the natives and the immigrant sick-leave periods were of shorter duration, the two study populations did not show differences in the causes of disability.