Assessing parenting stress in parents of children with autism has crucial clinical implications because increased parental stress is associated with psychological disorders and personal distress, which can result in worse child-parent relationships. We examined the psychometric properties of a new index for assessing parenting stressors--the Developmental Disorder Parenting Stressor Index and the temporal variability of parenting stressors using longitudinal data of 212 Japanese parents of children with autism aged 2-18 years. The findings indicated that the Developmental Disorder Parenting Stressor Index has appropriate cross-validity, structural validity, construct validity, and reliability. Moreover, the psychometric properties and the brevity of the Developmental Disorder Parenting Stressor Index increase the clinical utility of the scale. The implications of the findings of this study are discussed.