The diagnosis of poisoning is often obvious (e.g. in a patient presenting with drug overdose), but can sometimes be more challenging. This article describes some clinical presentations where poisoning should be considered in the differential diagnosis. These are unexplained coma or confusion, hypoglycaemia, abnormal liver function, unexplained convulsions, metabolic acidosis and abnormal bleeding. Poisoning should also be considered if several people present with similar symptoms or in children who have chronic, recurrent or unexplained symptoms.