OBJECTIVE To determine the independent associations of dietary preference for fat with obesity without the confounding by genetic effects. METHODS Descriptive comparison of the responses of monozygotic twins discordant for obesity to questions concerning current and past preference for dietary fat, current overconsumption of fatty items and recalled food consumption compared to the co-twin. METHODS The Research and Development Centre of the Social Insurance Institution, Finland. METHODS Twenty-three healthy monozygotic twin pairs who were discordant for obesity (BMI difference at least 3 kg/m(2)). METHODS Obesity status of the twin, as a function of the current and recalled dietary preferences and selected psychosocial variables. RESULTS The obese twins reported current preference for fatty foods three times more frequently than the lean co-twin. Moreover, when comparing recalled taste for fat at the time the twins left their parental homes, both the obese and lean co-twins consistently recalled that the obese twin had greater preference for fatty foods in young adulthood, and that the lean twin had less. Psychological characteristics of lean and obese co-twins did not differ. CONCLUSIONS Acquired preference for fatty foods is associated with obesity, independent of genetic background. Modification of fat preferences may be an important step in the prevention of obesity in the general population.