The association between single-parent family background and physical illness in early adulthood was studied in a sample of an unselected, general population: the Northern Finland 1966 Birth Cohort. Between the ages of 16 and 28 years, women of single-parent family background were more commonly treated (61% versus 57%) for any physical condition in hospital wards compared with women of two-parent family background. Spontaneous abortions (odds ratio; OR = 1.4, 95% CI 1.0-2.0), complications of pregnancy (OR = 1.1, 95% CI 1.0-1.3), and intracranial injuries (OR = 2.0, 95% CI 1.0-3.8) were more common among women with single-parent family background. They also had a clearly higher risk for induced abortions (OR = 1.6. 95% CI 1.4-1.9), and a higher incidence of deliveries than did other women. The risk of hospital-treated physical illness did not differ between men of single-parent and two-parent family background. Poisonings and injuries were, however, more common reasons for hospital admission among men with single-parent family background than among other men. In conclusion, our main finding was that, among women, an association between overall hospital-treated physical illness and single-parent family background does exist. However, offspring of single-parent families are mostly in as good physical health as others.