This prospective exploratory story examined diurnal variations in pulmonary function and their association with sleep and quality of life (QOL) in 20 adult asthmatics. Peak expiratory flow (PEF) was assessed for 7 days, before bedtime and upon awakening. There was no association between PEF variability and QOL. Six of 13 polysomnographic measures were significantly correlated with overnight decline in PEF. Individuals with greatest decline took longer to fall asleep and enter Stage 1 sleep, spent less time asleep, and experienced poorer sleep efficiency. Diurnal variations in PEF reflect adverse sleep quality, yet impact on QOL is often unnoticed.