This paper presents the results of an epidemiologic study that compares and contrasts psychosocial characteristics of parents and family units of children with chronic illness or physical disability (chronic health problems) with those of healthy children. Data were derived from the Ontario Child Health Study of 1869 randomly selected families, with 3294 children aged 4 to 16 years. In the absence of significant differences between parents and families of children with chronic illness alone and those with physical disability, these groups were combined for analysis, for which odds ratios (OR) or t tests were used. Significant positive findings included increased rates of parental treatment for "nerves" (mothers' OR = 2.1, fathers' OR = 1.9) and increased maternal negative affect scores (Bradburn Affect Balance Scale) (P less than .001) among parents of children with chronic health problems. Important negative findings (95% confidence interval of the OR included 1) included no increase in single-parent families (OR = 1.2), social isolation (OR = 1.0), or alcohol problems (OR = 1.2) among parents of children with chronic health problems. Categorically defined family dysfunction did not differ between the two groups (OR = 1.1). These data contrast with several clinic-based studies and suggest that, in a widely generalizable population survey, families of children with chronic health problems including physical disability do not suffer a marked excess of dysfunction, although some indicators of individual parent psychosocial problems were modestly elevated.(ABSTRACT TRUNCATED AT 250 WORDS)