Body image investigation is fundamental to assess body dysmorphic disorder (BDD). When dissatisfaction is related to the muscle, it is suggestive to be accompanied by muscle dysmorphia (MD) – with or without insight. In BDD, the presence of other comorbidities can make it difficult to diagnose the disorder. In this sense, this case report aimed to present the use of auxiliary methods to facilitate the diagnosis of MD in a patient with mental retardation. Two instruments were tested: Scale of Body Image (SBI) and Muscle Appearance Satisfaction Scale (Mass). Male, 33 years, completed primary school, single. Mild intellectual disability with a tendency to impulsive behavior. As for SBI, the participant identified himself with image 6, but he said he had the desire to resemble image 9. This discrepancy corroborates the suspicion of body image dissatisfaction. Regarding the Mass questionnaire, the score was 84: positive for MD. With this case report, we suggest the use of the instruments mentioned to help in the MD evaluation, especially in patients with low intellectual capacity, which have difficulties in mentioning their complaints. It is important to note that this application does not dispense analysis of clinical and psychological indicators.