Neonatal haemophagocytic lymphohistiocytosis (HLH) is a rare but potentially lethal condition. We recently encountered a preterm infant who developed severe HLH associated with maternal adult-onset Still's disease, which to our knowledge has not been previously reported. The infant presented with fever, generalised lymphadenopathy, transient erythematous skin rash, hepatosplenomegaly, ascites, pancytopenia, marked hyperferritinaemia, and hypofibrinogenaemia, which were features similar to maternal presentation during late pregnancy. Whole gene exome sequencing screening for familial HLH (PRF1, STX11, STXBP2, and MUNC13D genes) was negative. We postulated that factors such as auto-antibodies, antigens, or inflammatory mediators transmitted vertically from the mother could have triggered the intense inflammation in the infant. The infant responded promptly to dexamethasone, etoposide, and cyclosporin A, without the need for bone marrow transplantation. Neonatologists should be alerted to the rare diagnosis of HLH in the presence of active maternal diseases, including infection or autoimmune conditions, especially in association with fever, cytopenia, and hepatosplenomegaly.