School non-attendance in autism spectrum disorders has received very little attention to date. The study aimed to provide a comprehensive description of school non-attendance in students with autism spectrum disorders. Through an online survey, parents of 486 children (mean age: 11 years) reported on school attendance over 1 month and reasons for instances of non-attendance. On average, students missed 5 days of school of a possible 23 days. Persistent non-attendance (absent on 10%+ of available sessions) occurred among 43% of students. School non-attendance was associated with child older age, not living in a two-parent household, parental unemployment and, especially, attending a mainstream school. School refusal accounted for 43% of non-attendance. School exclusion and school withdrawal each accounted for 9% of absences. Truancy was almost non-existent. Non-problematic absenteeism (mostly related to medical appointments and illness) accounted for 32% of absences. Non-problematic absenteeism was more likely among those with intellectual disability, school refusal was more likely among older students and school exclusion was more likely among students from single-parent, unemployed and well-educated households. Findings suggest that school non-attendance in autism spectrum disorders is a significant issue, and that it is important to capture detail about attendance patterns and reasons for school non-attendance. Lay abstract Our study aimed to describe school non-attendance in students with autism. We conducted an online survey. Parents of 486 students (mean age: 11 years) indicated which days their child had missed school (over a period of 1 month). If the child had missed a day, the parent was asked to select a reason from a list of 15 possible reasons (this is a measure of types of school non-attendance called SNACK (School Non-Attendance ChecKlist; Heyne et al., 2019)). On average, students missed 5 days of school of a possible 23 days. Missing over 10% of school is known as persistent absence, and in our study, 43% of students experienced persistent absence. Older students, who attended mainstream schools, who did not live in a two-parent household and whose caregiver was unemployed were more likely to miss school. Looking at the reasons for absence, school refusal was the most frequent reason, accounting for 43% of absences. Nine percent of absence was due to school exclusion. Nine percent of absence was due to school withdrawal. Truancy was almost non-existent. A final reason describes non-problematic absence that is mostly due to medical appointments and illness. This type of absence accounted for 32% of absences in our study, and it was more likely in student with intellectual disability. School refusal was more likely among older students. School exclusion was more likely among students from single-parent, unemployed and well-educated households. Findings from this study help us to understand better the difficulties students with autism experience attending school.