The present study was conducted to determine whether smokers have more plaque than non-smokers, and whether higher plaque scores subsequently found in smokers could be explained by differences in toothbrushing time, efficiency and frequency. Plaque was scored from photographs, before and after toothbrushing, in 64 smokers and 64 non-smokers, aged 20-40 years, matched for age and sex. The results showed that in both sexes smokers had more plaque than non-smokers. Male smokers brushed for a shorter time, and had more plaque after toothbrushing, than male non-smokers. A similar, though non-significant trend was found in females. There was no association between tobacco consumption and frequency of toothbrushing. It was concluded that the poorer oral cleanliness found in smokers both before and after toothbrushing may be explained, in part at least, by their shorter toothbrushing time.