Aim of the study:
To better understand the origin of sleep quality impairment among psoriasis patients, we sought to examine whether the psoriasis severity, health related life quality, itch and depression are significant predictors of sleep disruption; and whether itch intensity and depression are mediators of the relationship between the health- related life quality and sleep problems.

Subject or material and methods:
42 patients diagnosed with chronic plaque psoriasis, (female: 40.5%; mean age=44.48 years; SD=17.57, age range=21-82) completed Polish versions of: the Pittsburgh Sleep Quality Index (PSQI), the Centre for Epidemiological Studies - Depression scale (CES-D). The itch intensity was measured according to the 10-point visual analogue scale (VAS). The Severity of patient’s psoriasis was evaluated by using The Psoriasis Area Severity Index (PASI), health related life quality was assessed using the Dermatology Life Quality Index (DLQI) .

Results:
The stronger the negative effect of psoriasis on patients’ life as measured by Dermatology Life Quality Index, the greater the sleep disturbances.

Discussion:
The results confirm that poor health- related quality of life may account for higher sleep ditrubances among psoriasis patients, and suggest that this negative effect reveals itself, through enhancing depression.

Conclusions:
It seems that a greater therapeutic focus on health related quality of life in psoriasis patients may lead to an improvement in their sleep quality.