Background Knowledge of school attendance problems (SAPs) is needed to inform treatments targeting SAPs and protecting youths from negative outcomes associated with SAPs. Objectives This study examined the school absence, absence categories (i.e., absence due to illness, excused, non-excused), sociodemographic characteristics, and mental health problems among youths seeking psychological treatment for SAPs. Methods The study used a cross-sectional design. Sociodemographic and clinical characteristics of 152 help-seeking youths with SAPs (i.e., >10% absenteeism) and their parents were examined. The data were derived from the baseline assessment conducted before treatment start. Results Older youths, youths with mental health problems, and youths whose parents had mental health problems exhibited higher levels of absence. Lower levels of non-excused absence were found among youths with highly educated fathers, and youths living with both parents. Many youths had clinical levels of anxiety, depression, or ‘emotional and behavioral difficulties’. Conclusion The study highlights the need for early intervention, addressing a broad range of mental health problems. Clinical trial registration ClinicalTrials.gov: NCT03459677.