Thinking negatively about one's appearance may be a major source of unhappiness. It was investigated whether the habitual quality of negative body image thinking constitutes an additional vulnerability factor, i.e. when such thinking is repetitive and automatic. The cognitive content of negative body image thinking (‘what’) was distinguished from the habitual occurrence of such thinking (‘how’). The mental habit component uniquely predicted explicit as well as implicit body dissatisfaction (the latter measured by an implicit association test) over and above cognitive content. Mental habit also accounted for eating disturbance propensity, low self-esteem and restrained snacking behaviour over and above cognitive content, even when controlled for body dissatisfaction. The habitual component of negative thinking about appearance thus seems a significant body image construct, has discriminant validity against body dissatisfaction, and constitutes a vulnerability factor for feelings of low self-worth and eating disturbance propensity. Implications for intervention strategies, such as mindfulness-based approaches, are discussed.