Hemophagocytic lymphohistiocytosis (HLH) is a rare and life-threatening disorder of excessive immune activation. It is mostly seen in the paediatric population and is rarely observed in adults. HLH can be inherited or acquired and is commonly triggered by activation of the immune system by an underlying viral infection or in immune system deficiency such as malignancy or underlying rheumatological disease. HLH is a difficult entity to diagnose due to the rarity of this disorder, variable clinical presentation and non-specific clinical and laboratory findings. HLH carries a high mortality if left untreated, and therefore prompt diagnosis and initiation of immunosuppressive, immunomodulatory and cytostatic medications are critical to improve survival in affected patients. Here, we present a case of lamotrigine-associated HLH. To our knowledge, only eight other cases of lamotrigine-associated HLH have been reported in adult patients. Copyright (c) BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.