Background: Psychosis is often solely described as a psychiatric presentation; however, it is vital that organic causes are eliminated, especially in children. Case presentation: We report the case of a 14yr old girl who presented two months history of self-neglect, poor school performance and a week history of mutism. At initial presentation, her neurological examination was normal except for expressive aphasia, and occasional inappropriate laughing. First line investigations showed low vitamin B12 and folate and normal MRI. She was planned for follow up with psychiatrists. She presented about a week later with worsening symptoms. She had further investigations which revealed high homocysteine, in keeping with homocysteine remethylation disorder. She started betaine therapy after which she had a significant improvement in her symptoms. Conclusion: This case emphasizes the importance of thorough investigations of children with acute psychosis before making an assumption of a psychiatric cause, as reversible causes have better outcomes.

Keywords: Keywords: Delusion, Hallucinations, Psychosis, Case report.