As shown first by stepwise multiple correlations and then by family "sets" the probability that a parent or a child will be obese is a direct function of the fatness level of remaining family members. For a four-member nuclear family the probability that one member will be obese is well below chance expectancy (i.e., 12.6%) if the remaining three members are all lean and far higher (i.e., 40.7%) if the remaining family members are all obese. While mothers follow family line fatness expectancy, there is an excess of obese mothers in lean nuclear families, consistent with the inverse relationship between adult female fatness and socioeconomic status.