Background: Correctly identifying oneself as being overweight is presumed to be a prerequisite to successful weight management. The present research examined the effect that perceiving oneself as being ‘overweight’ has on risk of future weight gain in US and UK adults. Methods: Data from three longitudinal studies; US National Longitudinal Study of Adolescent Health (Add Health) 2001/2002–2008/2009, UK National Child Development Study (NCDS) 1981–2002/2004, and Midlife in the United States (MIDUS) 1995/1996–2004/2005, were used to examine the impact of perceiving oneself as being overweight on weight gain across adulthood in over 14 000 US and UK adults. Results: Participants who perceived their weight status as being overweight were at an increased risk of subsequent weight gain. This effect was observed irrespective of weight status at baseline and whether weight status perceptions were accurate or inaccurate. In the MIDUS sample, perceiving oneself as being overweight was associated with overeating in response to stress and this mediated the relationship between perceived overweight and weight gain. Conclusions: Perceiving oneself as being ‘overweight’ is counter-intuitively associated with an increased risk of future weight gain among US and UK adults.