This article describes the assignment of dyslipoproteinemia (DLP) in several free-living North American populations and presents mean lipid and lipoprotein levels for each type. Dyslipoproteinemic phenotypes were assigned by a modified version of the National Institutes of Health (Fredrickson) phenotyping system. Criteria for assigning phenotypes included age- and sex-specific 5th and 95th percentiles for low-density lipoprotein and high-density lipoprotein cholesterol and total triglyceride, as well as other qualitative and quantitative criteria. Phenotypes IIb, III, I, and V were uncommon, confirming clinical impressions of their frequency. Lipid and lipoprotein levels in specific phenotypes were generally as expected. In the type III phenotype, however, mean cholesterol and triglyceride levels were surprisingly low. Gonadal hormone use, in the form of both oral contraceptives and postmenopausal estrogens, was reported in approximately 30% of women in these populations and was associated with dramatic differences in the frequency of DLP when compared with women not taking hormones. In general, these differences reflected the previously described effects of estrogen and progestins on lipoprotein levels. These data gathered in free-living populations: confirm clinical impressions of the rarity of some phenotypes, focus attention on those phenotypes in which diminished rather than elevated lipoproteins are found, and provide further evidence of the effect of hormones on lipid and lipoprotein levels.