We test for differences across the two most recent NHANES survey periods (1988-1994 and 1999-2004) in self-perception of weight status. We find that the probability of self-classifying as overweight is significantly lower on average in the more recent survey, for both men and women, controlling for objective weight status and other factors. Among women, the decline in the tendency to self-classify as overweight is concentrated in the 17-35 age range, and, within this range, is more pronounced among women with normal BMI than among those with overweight BMI. Among men, the shift away from feeling overweight is roughly equal across age groups, except that the oldest group (56-74) exhibits no difference between surveys. In addition, overweight men exhibit a sharper decline in feeling overweight than normal-weight men. Despite the declines in feeling overweight between surveys, weight misperception did not increase significantly for men and decreased by a sizable margin among women. The shifts in self-classification are not explained by differences between surveys in body fatness or waist circumference, nor by shifting demographics. We interpret the findings as evidence of a generational shift in social norms related to body weight, and propose various mechanisms to explain such a shift, including: (1) higher average adult BMI and adult obesity rates in the later survey cohort, (2) higher childhood obesity rates in the later survey cohort, and (3) public education campaigns promoting healthy body image. The welfare implications of the observed trends in self-classification are mixed.