Fragile X syndrome (FXS) is the most commonly detected single gene cause of intellectual disability (ID) and autism spectrum disorder (ASD). Comprehensive and multidisciplinary evaluation of patients with ID or ASD is essential for prudent management of any probable underlying condition. Herein we report a 4 years and 3 months old boy with speech delay, previously admitted to other clinics many times without any definite diagnosis. Physical examination revealed that he had hyperactivity, poor eye contact and dysmorphic features. He had global developmental delay and symptoms of ASD. The patient who had dysmorphic features was referred to pediatric genetics department with the suspicion of FXS. Southern Blot analysis revealed CGG repeat expansion in the range of full mutation. Maternal southern blot analysis revealed expanded CGG repeat in the range of premutation, and the family was given genetic counseling. The patient is still being followed-up at the developmental pediatrics department with an individual education program and other supportive treatments.Children with FXS typically present with developmental delay. Although motor delays are often seen, these tend to be mild, and affected males most commonly come to hospital because of speech delay as the patient in this case. The present patient has both FXS and ASD diagnosis. As children with FXS may not have gross physical features, any child who has developmental delay, borderline intellectual abilities, ID or ASD with an unknown etiology should undergo molecular testing for fragile X syndrome. It was aimed in this case to emphasize the importance of comprehensive and multidisciplinary evaluation of all patients referred with speech delay.