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Alkaptonuria (AKU) is a rare metabolic disorder resulting from deficiency of homogentisic acid (HGA) oxidase involved in the metabolism of tyrosine. Dark discolouration of urine, ochronosis at cartilage and connective tissues, arthritis at the third of fourth decade of life, cardiac valve deficits, renal stone disease, spontaneous tendon rupture, and liver involvement may be seen in alkaptonuria. It was reported that HGA oxidase gene was expressed in human cerebral tissue and neuronal cells in AKU with multi-systemic organ involvement. HGA accumulation has been implied and neurological problems and brain damage. To the best of our knowledge, there is no study or case report about psychiatric comorbidities in patients with AKU, although comorbid psychiatric disorders such as mental retardation, attentiondeficit/hyperactivity disorder (ADHD), impulse control disorder or conduct disorder can be seen in some metabolic diseases such as mucopolysaccharidosis, Wilson’s disease, or phenylketonuria. Here, we presented a paediatric AKU patient with comorbid ADHD, oppositional defiant/conduct disorder (ODD/CD), and borderline intellectual functioning who was successfully treated with extended-release methylphenidate (OROS-MPH) and risperidone. It was observed that these agents caused no worsening in AKU and that they were well-tolerated without adverse effects. However, there is a need for further studies investigating the safe use of OROS-MPH and risperidone in patients with AKU.