OBJECTIVES: To investigate the effect of an educational program for preventive healthcare professionals in routine primary care on functional ability, nursing home admissions, and mortality in older adults. DESIGN: A prospective, controlled 3-year follow-up study (1999-2001) in primary care with randomization and intervention at the municipality level and outcomes measured at the individual level in two age cohorts. SETTING: Primary care. PARTICIPANTS: Of 81 eligible municipalities in four counties, 34 agreed to participate. A total study population of 5,788 home-dwelling subjects aged 75 and 80 were asked to participate. Written consent was obtained from 4,060 persons (70.1%), of whom 2,104 were living in 17 intervention municipalities and 1,956 were living in 17 matched control municipalities. INTERVENTION: Intervention municipality visitors received ongoing education, and local general practitioners were introduced to a short geriatric assessment program early in the study period. Control municipalities visitors and general practitioners received no education. MEASUREMENTS: At the 3-year follow-up, the outcome measures of mortality and nursing home admissions were obtained from all, and the outcome measure of functional ability was obtained from 3,383 (95.6%) of 3,540 surviving participants. RESULTS: Education improved functional ability (odds ratio=1.20, 95% confidence interval (CI)=1.01-1.42, P=.04) in intervention municipality participants, notably in the 80-year-olds. There were no differences in mortality (relative risk (RR)=1.06, 95% CI=0.87-1.28, P=.59) or rates of nursing home admissions after 3 years (RR=0.74, 95% CI=0.50-1.09, P=.13). Subjects aged 80 benefited from accepting and receiving in-home assessment with regular follow-ups. CONCLUSION: A brief, feasible educational program for primary care professionals helps preserve older people's functional ability.