Introduction: Propionic acidaemia a rare organic acidaemia, is an autosomal recessive disease from deficiency of mitochondrial enzyme propionyl-CoA carboxylase, leading to accumulation of propionic acid and toxic metabolites. Case presentation: The subject male infant, third child born to consanguineous parents, showed reduced activity since birth. On examination, he was drowsy ,moderately dehydrated and had no acidotic breathing, hypotonia or organomegaly . He was initially managed as presumed sepsis with intravenous antibiotics, but with minimal improvement. Basic investigations including venous blood gas and cranial imaging were unremarkable. A maternal history of neonatal death due to a suspected metabolic disease in a previous sibling warranted metabolic evaluation. Acyl carnitine profile revealed elevated propionyl carnitine C3 = 17 .06 μM (0.2-4.0 μM), C3 /C2 = 2.88 μM (0.02-0.2 μM), C3 /C16 =8.97 μM (0.12-2.6 μM) . Urine screening for organic acids and blood for aminoacidopathies confirmed the diagnosis . At one month, re-presented with a febrile respiratory illness followed by drowsiness and reduced activity .Metabolic acidosis, pancytopenia (Hb 6.4 mg/dL) and marginal hypoglycaemia indicated a metabolic crisis, managed with fluid and electrolyte resuscitation. A transient neurodevelopmental regression was noted, with gradual improvement Conclusion: Clinical features usually manifest in the neonatal period and exhibit a wide clinical spectrum ranging from catastrophic metabolic decompensations in early infancy to lenient late onset presentations in childhood. Neonates present with nonspecific symptoms mimicking neonatal sepsis, encephalopathy or dehydration, creating diagnostic challenges.High suspicion in consanguinity or unexplained sibling deaths is crucial to detect and initiate early treatment which would prevent catastrophic permanent impairments.