Because of recent heightened epidemiologic interest in persons with very low cholesterol levels, we compared men and women at the lowest and middle deciles of plasma cholesterol in a large population study for multiple sociologic, biologic, and medical attributes. Two sex-specific age groups were studied, 30-54 years and 55-79 years. In general, comparisons between deciles for each of these four age-sex groups revealed only minor differences for demographic variables; systolic or diastolic blood pressure; fasting plasma glucose; weight; height; obesity; cigarette smoking; dietary eggs or milk; medications for hypertension, hyperglycemia, hyperuricemia, or hyperlipidemia; family history of myocardial infarction, diabetes, or stroke; and personal history of myocardial infarction, congestive heart failure, hypertension, or stroke. Thus, the lowest and the middle deciles of plasma cholesterol in this population shared similar sociologic, biologic, and medical profiles. One unexpected finding was somewhat more diabetics in the lowest decile , and greater obesity and triglyceride levels in the lowest decile diabetics compared to either lowest decile non-diabetics or middle decile diabetics, perhaps suggesting a metabolically distinct subset.