The purpose of this study is to contribute to knowledge about leader-based workplace health interventions by investigating changes in psychosocial working conditions and health in Norwegian and Swedish small-scale enterprises (SSEs). The study also aims to investigate whether there are differences between position, and countries. In total, 30 leaders and 149 coworkers in 34 SSEs participated in two intervention and two reference groups. Leaders and coworkers completed the validated questionnaires (Nordic Questionnaire on Positive Organizational Psychology ([N-POP]), Work Experience Measurement Scale (WEMS), and Salutogenic Health Indicator Scale (SHIS), which cover different psychosocial working conditions and health outcomes. The interventions were carried out by advisors from occupational health services (OHSs) over a one-year period and consisted of analyses of health and psychosocial working conditions, company visits, education and networking meetings, including information and tools on issues such as leadership, work environment and health, and leadership support. The statistical methods used included principal component analyses, reliability tests, paired sample t tests and three-way ANOVA. The results indicate a significant positive development concerning external job performance in the intervention groups. Regarding internal job performance, both the Norwegian intervention group and the reference group showed positive improvements. However, there were negative or nonsignificant developments for several of the psychosocial working conditions and health outcomes in the intervention groups. With regard to associations and interactions between the studied variables, there were significantly positive developments with regard to external job performance and sickness absences in the total intervention group. The study indicates that more thorough procedures and testing of leader-based interventions in SSEs are required.