Ornithine transcarbamylase (OTC) deficiency (OTCD), the most common urea cycle disorder, is an X-linked genetic disorder due to complete or partial lack of the OTC enzyme. Its clinical presentation depends on the degree of enzyme deficiency and ranges from an acute neonatal metabolic crisis with a high mortality rate through to an asymptomatic adult. We present a case of a newborn baby boy who presented with poor feeding, vomiting, lethargy, and respiratory distress. Laboratory investigations revealed severe hyperammonaemia, hyperglutaminaemia, hyperalaninaemia, absence of citrulline, and marked orotic aciduria. Family screening confirmed the presence of an OTC disease-causing mutation in his mother. It was a heterozygous mutation, c.316G>A. p. Gly106Arg in exon 4.