The study focuses on the theme of mental health and sexual self-concept. The objective was to validate and measure the Multidimensional Sexual Self-Concept Questionnaire for the Portuguese population, to compare differences in the levels of sexual self-concept and mental health in a clinical sample and in a non-clinical sample, to determine the predictive relationship between sexual selfconcept and mental health. A study of descriptive, operational, inferential and of transversal nature was carried out on two non-probabilistic samples. Sample A, 494 Internet users, mean age of 27.68 and standard deviation of 8.98; Sample B, 131 participants (mean age 36.8 and standard deviation 11.15), divided between 61 patients with clinical diagnosis from a Department of Psychiatry and Mental Health and 70 participants from the general population and without any psychopathology. As tools a socio-demographic questionnaire, a questionnaire about sexuality, the Multidimensional Questionnaire on Sexual Self -Concept (Snell, 1995) and the Mental Health Inventory (Pais Ribeiro, 2001) were used. All ethical issues were duly covered in legal and ethical terms. The psychometric validation of the Multidimensional Sexual Self -Concept Questionnaire indicated good sensitivity, excellent internal consistency (α = 0.91), excellent adequacy for factorial analysis (KMO = 0.95), and 5 dimensions taken from the factorial analysis with very high internal consistency, proving a good tool for measuring this construct. In the comparative study between the clinical and nonclinical samples, the clinical sample shows lower levels of mental health, reporting more anxiety, depression, loss of emotional and behavioral control and psychological distress; The clinical population has more negative emotions regarding sexual self-concept; Men seem to be more vigilant about sexual aspects; Those who report taking psychoactive drugs have lower levels of mental health (more anxiety, depression and psychological distress); Subjects with a lower educational level have lower levels of mental health and lower sexual self-concept; Individuals who are currently in a love relationship show more positive affect on mental health and suggest more emotional locus of control and less negative emotions about sexual self -concept; Those who reported having had sex last month had higher levels of mental health and higher sexual self -concept; Younger individuals exhibit higher levels of mental health and a higher sexual self-concept compared to older subjects. We can conclude that good mental health is a predictor of good sexual self -concept. We thus highlight the pertinence of mental health nursing intervention in health promotion.