A heightened cortisol awakening response (CAR) is associated with adiposity in middle-aged men, but the causal significance of this effect is not known. We hypothesised that if disturbance in cortisol secretion is involved in the development of overweight and obesity, then it might be present in normal weight adults at increased risk of obesity on account of parental adiposity. The CAR and cortisol profile over the day were measured in 33 men and 62 women aged 18-25 years. Parental adiposity was assessed with figure ratings derived from the Contour Drawing Rating Scale, and these were correlated with parental self-reported body mass index (BMI) in a subset of participants (r=0.66-0.79). In men, a positive association was observed between the CAR and their judgements of their fathers' adiposity after controlling for age, smoking status, time of waking, and the participants' own BMI; the correlation was 0.56 (P=0.008) for the cortisol increase between waking and 30 min, and 0.47 (P=0.028) for the cortisol area under the curve. The correlation between the CAR and fathers' own reported BMI and figures ratings were also significant. The relationship between parental adiposity and the CAR in women was inconsistent, and the associations between the CAR and opposite gender parental adiposity were not significant. Parental adiposity was not related to cortisol output over the rest of the day or to the slope between waking and evening in either sex. The results of this study suggest that disturbances of cortisol secretion may present before the emergence of heightened adiposity in young men at raised risk for obesity.