Background: The role of teachers is of fundamental importance in the life of school children. Several studies have shown teaching to be a stressful job associated with high psychiatric morbidity. Since it is important that teachers are in good mental health to perform their duties, efforts should be made to know their mental health status in order to be able to create awareness and make recommendations to policy makers on how to attain and maintain an optimum mental health status for school teachers. Objective: To determine the prevalence of psychiatric morbidity among secondary school teachers in Mainland LGA of Lagos State and to compare the findings with that of the staff of the same LGA. Methodology: The sample size comprised of 744 subjects which included 372 teachers and 372 staff of the LGA. The LG staffs were matched with the teachers for age, gender and socioeconomic status. All the subjects completed self-administered questionnaires on sociodemographic and occupational parameters. The subjects were screened for probable psychiatric morbidity using the self-administered General Health Questionnaire (GHQ)-30. The Present State Examination (PSE) was used to elicit symptoms and diagnoses were made using the International Classification of Mental and Behavioural Disorders, 10th edition (ICD-10) criteria. The data were analysed with the Statistical Package for Social Sciences, 15th edition (SPSS-15). Results: The study showed that the prevalence of psychiatric morbidity among teachers was significantly higher (26.3%) compared with that of LG staff (18.5%) (p = 0.000). The sociodemographic factors significantly associated with psychiatric morbidity in the teachers were younger age (p = 0.000), male gender (p = 0.002), being single (p = 0.000) and higher number of children (p = 0.000). Similarly, occupational factors such as fewer years of working experience (p = 0.000), heavy workload (p = 0.012), incompetence at work (p = 0.000), low wages (p = 0.001), irregularity of promotion (p = 0.000), physical assault at work (p = 0.001) and job insecurity (p = 0.000) were significantly associated with psychiatric morbidity in the teachers. Among these factors, those found to predict morbidity in teachers were being single (OR = 10.13, 95% [CI] = 4.28-23.97, p = 0.000), having 3 or more children (OR = 5.00, 95% [CI] = 0.09 - 0.43, p = 0.000), irregularity of promotion (OR = 5.05, 95% [CI] = 0.02 – 0.13, p = 0.000), incompetence at work (OR = 3.22, 95% [CI] = 0.06 – 0.86, p = 0.029) and of job insecurity (OR = 3.43, [CI] = 0.007- 0.106, p = 0.000). The most common disorder seen in both the teachers (46.4%) and the LG staff (43.1%) was depression of mild to moderate intensity. This was followed by General Anxiety Disorder (Teachers 28.9%, LG staff 34.7%) and Neurasthenia (Teachers 19.6%, LG staff 11.1%). Compared with LG staff, psychiatric morbidity was significantly higher among young (p = 0.000), male (p = 0.023), single (p = 0.000) teachers. Similarly, teachers with heavy workload (p = 0.000), who felt incompetent (p = 0.004) and with low wages (0.000) had significantly higher psychiatric morbidity compared with the LG staff. On the other hand, LG staff with poor relationships with senior colleagues had significantly higher psychiatric morbidity compared with the teachers (p = 0.000). Conclusion: The study showed that, the prevalence of psychiatric morbidity among secondary school teachers was higher than the comparison group. It is recommended that mental health educational programmes should be organized regularly for the teachers to increase awareness about mental health problems