In the Amsterdam Growth and Health Longitudinal Study (AGAHLS) biological risk factors for chronic diseases were measured on eight separate occasions over a period of 20 years in a group of apparently healthy males and females (n = 164). Data were first collected from participants at 13 years of age. At each of the eight measurements, a medical checkup was performed and participants were given information about their current health status based on their personal biological risk factor profile (cholesterol, blood pressure, body composition, and physical fitness). A comparable group (n = 113) was measured on two occasions only: at age 13 and again at age 33. It was hypothesized that the group with eight measurements would present a more favorable 20-year development of the risk factors than the group with only two measurements. In the present article the six additional measurements with personal feedback of one's health status were perceived as an "intervention," even though the AGAHLS never intended to improve the lifestyle or health of its subjects. The intervention appeared to have had a positive effect on body fat distribution and, in men, on systolic blood pressure. However, it was expected that these significant results were not true effects of the intervention, but that they were type-I errors. For the other variables, total cholesterol, high-density lipoprotein cholesterol, and the ratio between these two, for the sum of four skinfolds, diastolic blood pressure, neuromotor fitness, and for maximal oxygen uptake, the 20-year development did not differ between the two groups. Thus, the effects of a 20-year health measurement and information intervention begun in youth on biologic risk factors for chronic diseases were limited. The absence of clear significant findings may be due to the low contrast between the two groups, as only six intervention measurements were conducted over a period of 20 years. Another reason may be that the young and relatively healthy population under study here was not amenable to changing their fitness and health.