Background Agriculture is among the most hazardous industries in the United States. Methods A longitudinal study of injury among migrant Hispanic farm workers residing in six Northern California Migrant Family Housing Centers (MHCs) during the 1997 harvest season was conducted. Participants completed an initial interviewer-administered work-and-health questionnaire at the beginning of the harvest season addressing the preceding year; there were three periodic follow-up surveys. Results There were 1,201 adult farm workers (participation 85.2%) who completed the initial questionnaire. Of these, 837 (69.7%) completed the final follow-up survey. There were 86 agricultural injuries (incidence 9.3/100 full-time equivalent employees (FTEs), 95% CI 7.5-11.5/100 FTE). Increased risk for agricultural injury occurred among women paid piece-rate (RR 4.9, 95% CI 1.8-12.8). Sprains and strains were most common (31%), followed by lacerations (12%). Conclusions Agricultural injury experience in this cohort is comparable to that of agricultural workers in other U.S. settings. Increased risk among women paid piece-rate suggests further study and potential policy changes regarding payment regimens. Heterogeneity of injury in this population presents a major prevention challenge. In view of high frequency of strain and sprain injuries, ergonomic interventions deserve further study. (C) 2003 Wiley-Liss, Inc.