BackgroundTo evaluate outpatient healthcare expenditure associated with different levels of BMI and glucose metabolism alterations.MethodsThe study is based on a representative national sample of adults, with data obtained from electronic clinical records of 900 Italian general practitioners. Data relative to the year 2018 were analyzed. The study population was classified according to BMI (normal weight, overweight, and obesity classes 1, 2, and 3) and glucose metabolism status (normoglycemia – NGT; impaired fasting glucose – IFG; diabetes mellitus – DM). Outpatient health expenditures include diagnostic tests, specialist visits, and drugs.ResultsData relative to 991,917 adults were analyzed. Annual per capita expenditure rose from 252.2 Euro among individuals with normal weight to 752.9 Euro among those with class 3 obesity. The presence of obesity determined an excess cost, particularly among younger individuals. Within each BMI class, the presence of IFG or DM2 identified subgroups of individuals with substantially higher healthcare expenditures.ConclusionsOutpatient healthcare costs markedly increased with increasing BMI in all age categories, particularly among individuals below 65. Addressing the double burden of excess weight and hyperglycemia represents a significant challenge and a healthcare priority.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12913-023-09576-4.