Objective:The relationship between obesity and suicidal ideation and behavior (suicidality) is not well understood, and conventional suicide risk factors do not adequately explain the associations observed. Thus, the current study aimed to further examine the relationship between body mass index (BMI; kg m -2) and suicidal ideation as well as potential mechanisms of this relationship.Methods:Two hundred seventy-one adults (n=151 undergraduates; n=120 obesity treatment participants) completed self-report questionnaires assessing relevant variables, including suicidal ideation, perceived burdensomeness, thwarted belongingness and current height/weight used to calculate BMI.Results:There was a significant, quadratic relationship between BMI and suicidal ideation (b=0.001, t=2.21, P=0.03, partial r=0.14) and between BMI and perceived burdensomeness (b=0.003, t=2.50, P=0.013, partial r=0.16), such that as BMI increased, these positive associations became more pronounced. Additionally, perceived burdensomeness partially mediated the relationship between BMI and suicidal ideation.Conclusions:Individuals with a higher BMI demonstrated increased suicidal ideation as well as greater feelings of perceived burdensomeness. These results provide novel information regarding potential mechanisms explaining the obesity-suicidal ideation association. © 2013 Macmillan Publishers Limited.