Introduction and objectives: malnutrition remains an unrecognised problem in psychiatric centers. The aim of the present study was to find out the prevalence of malnutrition and to recognize the importance of diet in the nutrition of the mentally ill. Methods: the nutritional status of 65 patients was assessed by anthropometric measurements (weight, height, body mass index, tricipital skin fold, bicipital skin fold, subscapular skin fold, suprailiac skin fold, tibial skin fold, abdominal skin fold, waist-hip index, hip circumference and waist circumference), blood tests (ferritin, triglycerides, albumin, cholesterol, glucose), other variables (blood pressure), the MNA-2009 questionnaire, and the one-week menu. Personal data, sex, smoking habits, age, type of disease, physical activity, family visits and the variables included in the MNA-2009 questionnaire were also recorded for each patient. Results: the sample consisted of 13 women and 52 men, all of whom were mentally ill patients in a psychiatric institution. A total of 43.1 % were overweight and 21.5 % obese, with more women than men in each category. Regarding biochemical values, it was observed that triglyceride and cholesterol levels were higher than recommended values. In addition, they presented a great imbalance in macronutrients and micronutrients in the daily nutritional assessment. Conclusion: this study has demonstrated the high prevalence of malnutrition in psychiatric patients, in particular obesity, due to the large excess of each of the macronutrients and micronutrients in the daily menu of psychiatric patients.