In Ireland, over half the adult population are now considered to be overweight or obese. This has implications for individuals in terms of their health as well as for the health service in terms of care utilisation. Using SLAN (2007) data we estimate the impact on use of general practitioner (GP) services, hospital inpatient and hospital day case services of overweight and obesity. Our modelling approach accommodates potential unobserved heterogeneity associated with utilisation of primary and secondary health care. Controlling for a range of socio-demographic variables, we find that overweight and obesity are significant predictors of GP utilisation and obesity is a significant predictor of inpatient episodes. Translating increased utilisation into costs, primary health-care costs are estimated conservatively to be approximately (sic)17 million higher and secondary health-care costs approximately (sic)24 million higher in the Republic of Ireland as a result of overweight and obesity in adults. Given trends, overweight and obesity are likely to present an increasing challenge to the health service in the future that warrant further investigation.