Introduction: To examine the relationship between externalizing/ internalizing syndromes and school truancy among Form Four (10th grade) students attending "high-risk" schools in Kuala Lumpur. Methods: This is a cross-sectional study conducted upon 16-year-old adolescents attending three high-risk schools in Kuala Lumpur. A total of 373 students completed self-administered questionnaires on the sociodemographic variables and externalizing/internalizing syndromes. The number of truant-days per student during the study period was obtained from the school records. Results: The mean internalizing score, externalizing score and total problem score of those who were truant were found to be significantly higher (P < 0.05) than those who were non-truant. Multiple logistic regressions showed externalizing syndrome (odds ratio [OR] = 1.044; confidence interval [CI] = 1.012-1.078, P = 0.018) significantly predicts truancy but not the internalizing syndrome. Two other psychosocial factors, namely, having divorced parents (OR = 2.495, CI = 1.058-5.886, P = 0.037) and did not understand or were uncertain of the purpose of schooling (OR = 2.621, CI = 1.265-5.433, P = 0.010) were also showed to be stronger predictors of truancy compared to externalizing/internalizing syndromes. Discussion: Truancy has significant association to externalizing syndrome, in addition to other significant psychosocial variables like parental and schooling factors. This finding indicated the need for comprehensive assessment of students presenting with truant behavior, including the identification of associated psychological and behavioral problems which highlights the roles of mental health professionals in tackling truancy.