Firms must create, maintain and manage their corporate reputation to stay competitive. With the rise of social media and social network applications this management includes upholding the reputation online. Employees especially can harm companies’ reputation with thoughtless behaviour in social networks because their behaviour might be attributed to the firm’s products and services. This study investigates how employees’ behaviour in social networks affects customer outcome variables of corporate reputation such as trust and word of mouth. The study extends prior reputation research that centred on offline contexts and investigates reputation-related online behaviour of employees. The authors use an experimental design and surveyed 199 customers. The results indicate that employees’ reputable behaviour in social networks positively affect trust and word of mouth. Additionally, the authors find support for a mediating effect of customer-based corporate reputation. The findings contribute to corporate reputation research by enhancing our understanding of the effect of employee behaviour in social networks.