OBJECTIVE: To understand the impact of ankylosing spondylitis (AS) on presenteeism and to explore its relationship to sick leave. METHODS: AS patients completed a questionnaire consisting of sociodemographics, disease characteristics, and work outcomes, including sick leave and presenteeism, assessed by the Work Limitations Questionnaire (WLQ). Associations between a broad range of explanatory variables with the WLQ and AS-related sick leave were assessed by zero-inflated negative binomial and zero-inflated Poisson regressions. RESULTS: Of 311 employed patients (204 men [65.6%]), 18% had sick leave in the past month. Limitations in meeting time management demands (33.7%), physical demands (30.2%), mental-interpersonal demands (20.2%), and output (19.0%) were noted. With the mean ± SD WLQ index score of 6.7 ± 5.9, the average decrease in work productivity attributable to health was 6.3%; an extra 7.1% of work hours would be needed to compensate for lost productivity. Helplessness, female sex, and impaired health-related quality of life (Ankylosing Spondylitis Quality of Life instrument [ASQoL]) were major contributors to the level of presenteeism (P < 0.01). At-work limitations (WLQ) and lower quality of life (ASQoL) were significantly associated with probability of sick leave, while the length of sick leave was strongly associated with lower educational level and helplessness (P < 0.01), and in some models, also with disease duration and country of residence (P < 0.05). CONCLUSION: AS hinders patients' work, mainly in time management and physical demand domains. The WLQ and ASQoL are able to identify patients who incur sick leave. Helplessness contributes independently to the level of presenteeism and the length of sick leave.