The prevalence of comorbid psychiatric disorders among patients with eating disorders (ED) is higher than the general population. Individuals diagnosed with eating disorders have changes in their body mass index which could promote severe metabolic disruptions. This study aimed (1) to report the prevalence of comorbid psychiatric disorders among a Mexican adolescent sample diagnosed with eating disorders, (2) to compare our results with the prevalence of psychiatric disorders reported from a national survey of mental health of adolescents, (3) to compare the presence of psychiatric comorbidities between ED diagnoses, and (4) to explore the relationship of these comorbidities with the body mass index. In the study, we included 187 Mexican adolescents diagnosed with eating disorders. The psychiatric comorbidities were evaluated using the Mini International Neuropsychiatric Interview for children/adolescents, and a revised questionnaire on eating and weight patterns. We found that 89% of the Mexican adolescents diagnosed with ED had another psychiatric comorbidity. Major depressive disorder (52.40%) and suicide risk (40%) were the most prevalent comorbidities. Attention and deficit hyperactivity disorder (ADHD) prevalence was different between ED diagnosis, and adolescents with binge-eating disorder and ADHD had the higher body mass index. Our results showed that in this sample of Mexican adolescents, the presence of comorbidities could impact body mass index. This emphasizes the importance that clinicians take into consideration the presence of psychiatric comorbidities to achieve an integrative treatment for adolescents diagnosed with ED.