OBJECTIVES To estimate the number and cost of asthma-related productivity loss days due to absenteeism and presenteeism in Alberta in 2005. METHODS Using data from the 2005 Canadian Community Health Survey, this study focused on people of working age (18–64 years). Total asthma-related disability days, including in-bed days and activity-restricted days, were estimated by multiplying the difference in the means of total disability days between asthmatics and non-asthmatics adjusted for socio-demographic characteristics and other health conditions by a multivariate linear regression, with the number of asthmatics in the population. Number of productivity loss days was a sum between the number of in-bed days (absenteeism) and the number of activity-restricted days multiplied by a reduction in functional level (presenteeism), adjusted for 5 working days per week. Other data from Alberta or Canadian published literature, such as a reduction in functional level of 20%–30%, a labour participation rate of 73%, and an average wage of $158 per day in 2005, were also used for analyses. RESULTS The prevalence of asthma was estimated at 8.5% among approximately 2.1 million people of working age in Alberta in 2005. The difference in the means of total disability days between asthmatics and non-asthmatics was 0.487 (95%CI: 0.286–0.666) in a period of two weeks or 12.7 (7.5–17.9) in one year. With the reduction in functional level of 20%–30%, the number of asthma-related productivity loss days was estimated from 442 (259–624) to 533 (313–753) thousand, respectively. The corresponding cost was from $70 ($41–$99) to $84 ($49–$119) million. Of these, the presenteeism accounted for 42% to 52%. CONCLUSIONS An improvement in controlling asthma could have a significant economic impact in Alberta. Presenteeism plays an important role in asthma-related productivity losses and therefore employers should not only pay attention to absenteeism, but also to presenteeism, to minimize productivity loss.