OBJECTIVE To investigate actual and perceived disease control in Australians with asthma, and identify factors associated with overestimation of asthma control. METHODS This was a cross-sectional study of Australian adults with asthma, who were recruited via Facebook to complete an online survey. The survey included basic demographic questions, and validated tools assessing asthma knowledge, medication adherence, medicine beliefs, illness perception and asthma control. Items that measured symptoms and frequency of reliever medication use were compared to respondents' self-rating of their own asthma control. Predictors of overestimation of asthma control were determined using multivariate logistic regression. RESULTS Of 2971 survey responses, 1950 (65.6%) were complete and eligible for inclusion. Overestimation of control was apparent in 45.9% of respondents. Factors independently associated with overestimation of asthma control included education level (OR = 0.755, 95% CI: 0.612-0.931, P = 0.009), asthma knowledge (OR = 0.942, 95% CI: 0.892-0.994, P = 0.029), total asthma control, (OR = 0.842, 95% CI: 0.818-0.867, P < 0.001), agreement that most medications are addictive (OR = 1.144, 95% CI: 1.017-1.287, P = 0.025), and increased feelings of control over asthma (OR = 1.261, 95% CI: 1.191-1.335), P < 0.001). CONCLUSIONS Overestimation of asthma control remains a significant issue in Australians with asthma. The study highlights the importance of encouraging patients to express their feelings about asthma control and beliefs about medicines, and to be more forthcoming with their asthma symptoms. This would help to reveal any discrepancies between perceived and actual asthma control.