Elevated fibrinogen level is a predictor of cardiovascular disease in adults, and it is associated with sleep-disordered breathing. Levels of fibrinogen in adults are affected by other co-existing cardiovascular risk factors, which are not usually present in children. To investigate the association between fibrinogen and sleep-disordered breathing, a case-control study was carried out in children with and without habitual snoring. All snoring children underwent polysomnography. Morning fibrinogen values in 30 children with snoring and an apnoea-hypopnoea index (AHI) > or =5 episodes x h(-1) (median (interquartile range) 318 mg x dL(-1) (290-374)) were similar to values in 61 children with snoring and an AHI <5 episodes x h(-1) (307 (269-346)). Both groups had higher fibrinogen values than those in 23 controls without snoring (271 mg x dL(-1) (244-294)). There was no correlation between fibrinogen values and AHI, respiratory movement/arousal index or haemoglobin desaturation index. In conclusion, fibrinogen values are higher in children with snoring than in controls, but there is no association between these values and polysomnography indices.