Purpose: It is known that strong feelings of self-efficacy are linked with better management of asthma. However, it is not known whether the experience of poverty can detrimentally impact the self-efficacy feelings of asthma patients. This paper aims to determine whether falling into income or multidimensional poverty lowers self-efficacy among people diagnosed with asthma. Methods: Longitudinal analysis of Waves 7 to 11 (2007 to 2011) of the nationally representative Household, Income and Labour Dynamics in Australia (HILDA) survey using generalized linear models. The analysis was limited to those who had been diagnosed with asthma. The Freedom Poverty Measure was used to identify those in multidimensional poverty. Results: People with asthma who fell into income poverty had significantly lower self-efficacy scores-23% lower (95% CI: -35.1 to -9.1), after falling into income poverty for 3 or 4 years between 2007 and 2011 compared to those who were never in income poverty. Those who fell into multidimensional poverty also had significantly lower self-efficacy scores-25% lower (95% CI: -42.8 to -2.0), after being in multidimensional poverty for 3 or 4 years between 2007 and 2011 compared to those who were never in poverty. Conclusions: Asthmatics who fall into poverty are likely to experience a decline in their feelings of self-efficacy. The findings of this study show that experiencing poverty should be a flag to identify those who may need extra assistance in managing their condition.