OBJECTIVE--To investigate pretrial risk factors and long term mortality (1964-1992) in participants and non-participants of a multifactorial primary prevention trial. DESIGN--A prospective study among 3313 initially healthy businessmen. During the 1960s (1964 onwards), 3490 healthy male business executives born between 1919 and 1934 participated in voluntary health checks at the Institute of Occupational Health in Helsinki. From that period cardiovascular disease (CVD) risk factors were available in 3313 men. In the beginning of the 1970s these men were invited to join a multifactorial primary prevention trial of CVD. Six groups were formed: (I) healthy participants in a high risk intervention group (n = 612), and (II) their randomised control group (n = 610); (III) a non-participant low risk group (n = 593); (IV) an excluded group with signs of CVD (n = 563); (V) a refused group (n = 867); and (VI) dead (n = 68). Groups I and II participated in the five year prevention trial which started in 1974. Other groups were followed up through registers, with no personal contact. MEASUREMENTS--Cardiovascular risk factors during the 1960s. Mortality follow up using national registers up to 31 December, 1992. MAIN RESULTS--Baseline risk factors were lowest in the low risk group, highest in the excluded group, intermediate and comparable in other groups. Eighteen-year (1974-1992) mortality (per 1000) was 79.3, 106.6, 155.2, 179.9, and 259.3 in the low risk, control, intervention, refused, and excluded groups, respectively (P < 0.001). In the whole population of 3313 men, the 28-year (1964-1992) total (n = 577) and coronary deaths (n = 199) were significantly predicted by smoking, blood pressure, and cholesterol; cancer deaths (n = 163) by smoking only; and violent deaths (n = 83) by none of the risk factors. One-hour postload glucose was significantly associated with total mortality in the intervention group only. When the intervention and control groups were included in the same model, the effect of group on total mortality tended to be dependent on the 1 h blood glucose value (P = 0.06 for the group by 1 h glucose interaction term). CONCLUSION--The traditional risk factors (smoking, blood pressure, and cholesterol) are significantly associated with 28-year mortality in this high social class population with previous health education. Conversely, a "clustering" of low risk factors predicted low total, coronary, and cancer mortality. The findings on 1 h blood glucose suggest that factors related to glucose tolerance explain in part the excess mortality in the intervention group compared with the control group.