Research has demonstrated that a self-defeating humor style is related to indicators of psychopathology and interpersonal dysfunction, including depression, anxiety, loneliness, thwarted belongingness, and perceived burdensomeness. The current study continued this investigation by examining how self-defeating humor is related to suicidal ideation and a ruminative response style. Analyses indicated that a self-defeating humor style was positively associated to rumination, brooding, reflection, and suicidal ideation. Results of bootstrapping analyses indicated that self-defeating humor mediated the relationship between rumination and suicidal ideation. This same effect was seen for both brooding and reflection individually. Results indicate that self-defeating humor may serve as an interpersonal means of ruminating as this humor style involves consistent focus on perceived flaws and weaknesses. The assessment of this humor style may provide additional information about the maintenance of suicidal thinking.