Introduction and objective: Our aim was to examine the secular trends in obesity prevalence among Spanish adults with diabetes. Material and methods: Data were collected from 8 waves (from 1987 to 2012) of the National Health Surveys (NHS). NHS are cross-sectional studies conducted in representative samples of the Spanish adult population. Data of 7378 adults (>= 16 years) who reported having been diagnosed of diabetes were analyzed. Previously validated self-reported weight and height were used to estimate body mass index (BMI). Obesity was defined as a BMI of 30 kg/m(2) or greater. Age-adjusted obesity prevalence for each wave was calculated by the direct standardization method. Results: From 1987 to 2012 age-adjusted prevalence of obesity among persons with diabetes increased from 18.2% (95% confidence interval [CI]: 14.2-22.2%) to 39.8% (95% CI: 36.8-42.8%). Age-adjusted prevalence of obesity in males with diabetes increased from 13.2% (95% CI: 7.3-19.1%) to 38.0% (95% CI: 33.8-42.1%) and in females from 23.0% (95% CI: 17.6-28.4%) to 42.3% (95% CI: 38.0-46.6%). Conclusions: Between 1987 and 2012 the prevalence of obesity markedly increased in Spain among adults with diabetes. (C) 2018 Elsevier Espana, S.L.U. All rights reserved.