Background: Mothers of children with autism experience high levels of stress. However, little is known about whether maternal stressors differ across children of different ages. Method: This study investigated stressors in mothers of 29 pre-school-aged and 27 school-aged children with autism. Correlation and regression analyses were used to determine if maternal stressors differed between the two age groups. Results: Findings revealed no difference in maternal stress levels across the two age groups; however, stressors for each age group were different. Stressors in the school-aged group were related to repetitive behaviours, sensory sensitivities, and problematic behaviours, while stressors in the pre-school-aged group were mainly related to adaptive behaviours. Conclusions: These findings are informative for practitioners and highlight the need for tailored supports and therapies for mothers of children with autism of different ages.