Klein and Boals (2001a, Applied Cognitive Psychology, 15[5], 565-579, Experiments 1 and 2) found that working memory capacity correlated negatively with perceived negative life event stress and speculated the relation may be driven by thoughts produced from these experiences. Here, we sought to replicate the association between working memory capacity and perceived negative life experience and to assess potential mediators of this association such as mind wandering propensity, rumination propensity, and the sum of negatively valenced mind wandering reports. In this preregistered replication and extension study, with data collected from 356 subjects (ns differ among analyses), we found no evidence suggesting that perceived negative life stress is associated with working memory capacity. Additionally, we found evidence consistent with the claim that negatively valenced mind wandering is uniquely detrimental to cognitive task performance, but we highlight a potential confound that may account for this association that should be addressed in future work.