The relationship between perfectionism and insomnia was studied by means of a shortened version of Frost et al's (1990) Multidimensional Perfectionism Scale (MPS-20). In the first study, an age- and sex-stratified sample of 383 randomly selected individuals from Uppsala, Sweden answered the MPS-20 and a number of questions about their sleep. Within this normal sample, perfectionism correlated with degree of sleep problem, and with an increased concern over the adverse consequences of insufficient sleep. In the second study, the MPS-20 was administered to a consecutive series of 70 patients with persistent insomnia from a sleep disorders clinic. This group was found to have significantly higher scores than the normals on perfectionism, and especially on the subscales Concern over Mistakes and Personal Standards. Within the insomnia group, patients with a concomitant diagnosis of major depression differed from the non-depressed insomniacs by having higher scores on the subscale Doubts about Action. Although these studies show a correlation between perfectionism and insomnia, they do not demonstrate a causal relationship. It is hypothesized that perfectionism (high personal standards and high concern over mistakes) may serve as a predisposing factor for the development of persistent insomnia.