Objective: Clinicians are less familiar with clinical presentation of rare disorder like mucopolysaccharidosis (MPS), especially as presentation is complex and varied with different subtypes of this disorder. This case report highlights severe behavioural problems and non-recognition of MPS by clinicians. Though behavioural problems, hyperactivity and aggression are common in children suffering from mental disability, they are also seen in rare metabolic disorders like MPS. Methods: We have reported a seven year old girl who presented with severe episodes of hyperactivity, poor social interaction, impaired understanding of speech and delay as well as regression in developmental milestones is presented along with the investigations and treatment given. Results: Initially, the child was thought to be suffering from intellectual subnormality and/or pervasive developmental disorder. However, radiological studies showed x-ray findings suggestive of MPS. Her developmental history, physical findings, hearing loss as noted on BERA further supported this diagnosis. Due to financial constraints of the family detailed investigations (enzyme assays) to know the exact type of MPS could not be done. Behavioural problems had to be managed with low dose clonazepam and carbamazepine. Conclusion: It is worth considering metabolic disorders as one of the important differential diagnosis in any child presenting with developmental problems, dysmorphic facies along with behavioural problems.