The aim of this study was to examine the severity of the symptoms of depression, anxiety, and stress in a nationally representative sample of secondary boarding school counselors and their association with sociodemographics, school counselor self-efficacy, self-esteem, happiness, and stressful life events. Participants consisted of 181 (52.5% women; M = 26.91) school counselors working at different secondary boarding schools across Turkey who completed the measures related to sociodemographics, happiness, self-esteem, school counselor self-efficacy, stressful life events, depression, anxiety, and stress. After confirming construct validity and reliability of the self-esteem, depression, anxiety, and stress scales, data were analyzed using descriptive statistics, Pearson product moment correlation analysis, and multivariate multiple regression analysis. The study results suggested that depression, anxiety, and stress symptoms are prevalent among school counselors, approximately 23% of whom experience at least moderate symptoms of depression and stress, and approximately 31% experience at least moderate symptoms of anxiety. Moreover, the results indicated that the most commonly experienced symptoms were dysphoria in depression, situational anxiety in anxiety, and impatience in stress among school counselors. This study also found that sociodemographic factors and school counselor self-efficacy were not associated with symptoms of depression, anxiety, and stress. However, higher levels of happiness and self-esteem and fewer stressful life events experienced within the past year consistently showed a negative association with exhibiting decreased symptoms of depression, anxiety, and stress among school counselors. Self-care activities focusing on increasing self-esteem and happiness and teaching skills to cope effectively with stressful life events may help to diminish the symptoms of depression, anxiety, and stress among secondary boarding school counselors.