Background. Excess body weight among adults is associated with increased risk of disease. Therefore, we sought predictors of weight gain that might be used to prevent increases in weight. Methods. Participants were 438 male fire service personnel, 20-58 years of age, who filled out a questionnaire in 1984 and were weighed in 1984 and 1991. Results. Sixty-five percent gained greater than or equal to 5 Ib, 42.1% gained greater than or equal to 10 Ib, and 26.1% gained greater than or equal to 15 Ib. Unmarried fire fighters gained 11.7 Ib; those married or living as married gained 7.0 Ib (P < 0.001). Black non-Hispanics increased by 15.7 Ib, white Hispanics by 8.9 Ib, and white non-Hispanics by 6.7 Ib 8 < 0.001). New ex-smokers gained 13.0 Ib; all other fire fighters gained 7.7 Ib (P < 0.004). Fire fighters who reported eating ''faster'' at the station than elsewhere gained 9.9 Ib compared with 6.8 Ib for all others (P < 0.006). Those worried over financial security gained 11.2 Ib versus nonworriers who gained 7.4 Ib (P < 0.005). Conclusion. Prevention programs will reach fire fighters likely to gain the most weight if aimed at those who are unmarried, younger, black, recent ex-smokers, fast eaters, and experiencing certain stressful life events. (C) 1996 Academic Press, Inc .