Objective: To report a case of a 12-year-old boy with intellectual disability and attention deficit hyperactivity disorder, who came to surgery for an examination due to a minor bulge on the left thumb, which had been growing for the previous month. His mother denied any trauma. Methods: After the removal of the clinically ambiguous bulge and a pathohistological confirmation that it was a periungual fibroma, complete patient analysis was performed due to the presence of hypomelanotic macules and a suspected tuberous sclerosis. Results: Considering the presence of hypomelanotic macules, as one of the main criteria, possible TS diagnosis was set. Conclusion: Early detection of the symptoms of TS enables a timely provision of protocols for further patient monitoring, which affects the patient’s morbidity and mortality.