Our aim was to examine the longitudinal associations between obesity and mental health variables (psychiatric diagnoses and suicidal behaviors). Data were from waves 3 and 4 of the Baltimore Epidemiologic Catchment Area study (N = 1071). Participants were aged 30 to 86 years at wave 3 (mean, 47.6 years; SD, 12.8). The prevalence of obesity increased from 27.6% to 39.1% during the follow-up. Logistic regression analyses revealed no associations between baseline obesity and onset of mental disorders or suicidal behaviors between waves 3 and 4 in fully adjusted models; however, baseline obesity predicted new-onset suicide attempts in models adjusted for sociodemographics and mental disorders. Baseline depression predicted weight gain during the 11-year follow-up period (F = 4.014, p < 0.05), even after controlling for important confounders. Overall, most mental health variables were not associated with obesity, suggesting that clinicians and others should be wary of "weight-ism" and avoid making the assumption that higher body weight relates to mental health problems.