We analyzed genetic and environmental determinants of self-rated health and its change from adolescence to early adulthood. Questionnaires were mailed to Finnish twins born 1975-1979 at ages 16, 17, 181/2 and, on average, 25 years of age (N = 2465 complete twin pairs). The data were analyzed using quantitative genetic methods for twin data by the Mx statistical package. Heritability of self-rated health was greatest at age 16 (63%, 95% confidence intervals (CI) 56-67%, men and women together) and declined steadily to age 25 (33%, 95% CI 25-41%). The residual variation was due to unshared environments. Health ratings at different ages were modestly correlated (r = 0.33-0.61). These correlations were mainly due to genetic factors, but unshared environment also contributed to them. An important challenge for further research is to identify environmental influences contributing to self-rated health independently of, or in interaction with, genetic factors. © 2006 Springer Science+Business Media, Inc.