While the number of diabetes-specific mobile applications (apps) continues to grow, there is a lack of knowledge about their actual use. The second MILES (Management and Impact for Long-term Empowerment and Success)-Australia study was a national cross-sectional survey of the psychological, behavioral, and social aspects of diabetes for adults with type 1 diabetes (T1D) and type 2 diabetes (T2D). Associations between diabetes-specific app usage and demographic, clinical, and psychosocial variables were examined. Of the 1589 respondents responding to the diabetes-specific app questions, 795 had T1D (mean ± standard deviation age 43 ± 14 years; 61% women; diabetes duration 19 ± 14 years) and 794 had T2D (age 60 ± 9 years; 40% women; diabetes duration 11 ± 7 years). Among adults with T1D, 24% (n = 188) reported using apps, with carbohydrate counting (74%; n = 139) as the most common cited purpose. App usage was significantly associated with shorter diabetes duration, more frequent glucose monitoring, and lower self-reported HbA1c. Among adults with T2D, 8% (n = 64) reported using apps, with glucose monitoring (62%; n = 39) as the most common purpose. For all respondents, the most commonly reported reason for not using apps was a belief that they could not help with diabetes self-management. A minority of adults with T1D and T2D use apps to support their self-management. App use among adults with T1D is associated with a more recent T1D diagnosis, more frequent glucose monitoring, and lower self-reported HbA1c. Future efforts should focus on this association and determine the mechanisms by which app use is related to better clinical outcomes.