Adult weight gain and central obesity can increase breast cancer risk. We determined the prevalence of adult weight gain and central obesity amongst women with a family history (FH) as compared to women with a population risk to determine whether adiposity could contribute to their increased risk. Adult weight gain, waist and waist:hip ratio (WHR) were determined amongst 475 women (aged 20–60 years) attending a regional FH breast cancer risk clinic, compared to 312 age matched women at population risk. Patterns of adult weight gain did not differ between women with and without a FH of breast cancer. The majority of weight gain occurred between the ages of 20 and 40 in both groups. Mean (sd) weight gain for women aged >40 years with a FH was 8.9 (10.3) kg compared to 9.1 (10.6) kg for controls (p = 0.85). Women with a FH had a significantly greater waist and WHR than controls. Mean (sd) waist was 83.7 (13) cm compared to 81.6 (11.3) cm for controls (p < 0.01). Mean (sd) WHR was 0.82 (0.1) compared to 0.80 (0.1) for controls (p < 0.01). FH of breast cancer was an independent predictor of having a WHR of >0.85; odds ratio (95% CI) = 1.42 (1.01–2.01) (p = 0.044). Significant weight gain between the ages of 20 and 40 and the prevalence of central obesity amongst FH women suggest the need for weight management within FH clinics.