Growth hormone replacement in adult growth hormone deficient patients improves psychological well-being and the quality of life. The aim of this study was to investigate relationship between changes in mood, cognitive functioning, quality of life, changes in body composition and hormone concentration at baseline and six months after treatment with human recombinant growth hormone. Eighteen adult patients with growth hormone deficiency syndrome were recruited to the study. Growth hormone was administered in doses of 12 IU per week in an open design. After 6 months of growth hormone replacement therapy the psychological functioning improved significantly on mood scales (Profile of Mood State) and on a cognitive performance tests. Changes in quality of life scale were trivial. After growth hormone treatment serum concentration of Insulin like growth factor -1 (IGF-1) and triiodothyronine increased and concentration of serum free thyroxine decreased significantly in comparison to basal concentration. There were no significant differences in changes of plasma cortisol, thyrotropin and growth hormone concentrations. Improvement on Profile of Mood State global score as well as on Vigor-Activity subscale correlated significantly with increase in IGF-1 concentration. Improvement on Profile of Mood State Vigor-Activity subscale correlated with increase in water body mass and improvement on Hospital Anxiety and Depression scale depression subscale correlated with decrease in cortisol concentration. The study shows that growth hormone replacement improves mood and cognition in adult growth hormone deficient patients. This improvement is related to changes in water body mass as well as to endocrine changes.