BACKGROUND: Clinical experience suggests that some adults who undergo bariatric surgery have children who are obese. Childhood obesity is associated with increased morbidity and mortality in later life. This study examined the prevalence of obesity among children and grandchildren (=12 years of age) of adult bariatric surgery patients. METHODS: Patients in a prospective database of morbidly obese patients who underwent bariatric surgery between January 2004 and May 2007 were recruited by phone and in clinic. Patient demographics, body mass index (BMI) at surgery, and survey data were collected. The survey included questions regarding their child/grandchild's body habitus, weight, and height. Child obesity was defined as BMI percentile >/=95. Statistical significance was set at p < 0.05. RESULTS: One hundred twenty-two patients were enrolled in this study (77% women, mean BMI 49 kg/m(2)). One hundred thirty-four out of 233 children/grandchildren identified had complete data; 41% had a BMI percentile >/=95. Only 29% of these obese children were so identified by the adult respondents. Significantly more biological children/grandchildren were obese than nonbiological (p = 0.013), and significantly more biological children were obese than biological grandchildren (p = 0.027). CONCLUSIONS: This sample of bariatric surgery patients had a high proportion of obese preteen children/grandchildren. Obesity was most prevalent among biological children (vs. biological grandchildren and nonbiological children). Patients often did not recognize the degree of overweight in their children/grandchildren. Because families of bariatric surgery patients often include obese children, interventions aimed at all family members merit consideration.