Online employer review platforms (ERPs) enable employees to evaluate their current and former companies anonymously online. Job-seekers can use the aggregated reviews to obtain information about potentially attractive companies and thus limit the number of suitable companies. However, the matching process between job-seekers and companies can only be effective if the information provided on ERPs is representative and can be trusted. This paper investigates specific characteristics of ERPs using the two large ERPs Kununu and Glassdoor as examples. It is argued that the ERP environment is very different from the well-known and -studied reputation system environment of online marketplaces, and that specific factors can potentially bias reviews on ERPs. Based on a new data set containing the Kununu and Glassdoor reviews of 114 major German employers, it is analyzed if and how design aspects of ERPs and other specific factors affect reviews. Results show that overall (and industry-specific), average review scores on Kununu and Glassdoor differ significantly from each other. Further results indicate that factors such as employees’ awareness of their impact on a company’s reputation also affect reviews. Suggestions are made on how ERPs could reduce the influence of these factors in order to present the aggregated information more effectively.