Objective: To investigate the relationship between work and quality of life (QOL) in patients with rheumatoid arthritis (RA) and ankylosing spondylitis (AS) aged 16-59. Methods: 1056 patients with RA and 658 with AS were included in the study. Data were obtained by postal questionnaire, which included severa generic and disease related QOL instruments. Separate dimensions and physical and mental summary scores from the SF-36 were compared. Stepwise multiple regression was performed to study the relationship between work and physical and mental health related QOL, including disease related factors, coping, and fatigue. Results: Physical health related QOL was reported to be worse, and mental health related QOL better, in RA than in AS in people of working age. No differences between RA and AS were found in somatic pain, physical role functioning, social functioning, emotional role functioning, vitality, or general health perception; nor were there any significant differences in fatigue and behavioural coping styles. Work was positively associated with physical health related QOL in both groups and, after disease characteristics, was the most important determinant. No association was found with mental health related QOL. Conclusions: Although physical health related QOL was worse in patients with RA, the impact on several dimensions of health related QOL in patients with RA and AS of working age under rheumatologica care was comparable. Patients with RA and AS experienced similar limitations in physical role functioning, including work. Work is an important independent external determinant of physical health related QOL, but not of mental health related QOL.