The impact of raising a child with autism spectrum disorder (ASD) is frequently accompanied by elevated caregiver stress. Examining the variables that predict these elevated rates will help us understand how caregiver stress is impacted by and impacts child behaviors. This study explored how restricted and repetitive behaviors (RRBs) contributed concurrently and longitudinally to caregiver stress in a large sample of preschoolers with ASD using parallel process multilevel growth models. Results indicated that initial rates of and change in RRBs predicted fluctuations in caregiver stress over time. When caregivers reported increased child RRBs, this was mirrored by increases in caregiver stress. Our data support the importance of targeted treatments for RRBs as change in this domain may lead to improvements in caregiver wellbeing.