The objective of the present study was to examine anthropometric, metabolic, psychosocial and dietary factors associated with dropout in a 6-month weight loss intervention aimed at reducing body weight by 10 %. The study sample included 137 sedentary, overweight and obese postmenopausal women, participating in a weight loss intervention that consisted of either energy restriction (ER) or ER with resistance training (ER+RT). Anthropometric (BMI, percent lean body mass, percent fat mass, visceral adipose tissue and waist circumference), metabolic (total energy expenditure, RMR, insulin sensitivity and fasting plasma levels of leptin and ghrelin), psychosocial (body esteem, self-esteem, stress, dietary restraint, disinhibition, hunger, quality of life, self-efficacy, perceived benefits for controlling weight and perceived risk) and dietary (3-d food record) variables were measured. Thirty subjects out of 137 dropped out of the weight loss programme (22 %), with no significant differences in dropout rates between those in the ER and the ER+RT groups. Overall, amount of weight loss was significantly lower in dropouts than in completers ( − 1·7 (sd 3·5) v. − 5·6 (sd 4·3) kg, P < 0·05); weekly weight loss during the first 4 weeks was also significantly lower. Dropouts consumed fewer fruit servings than completers (1·7 (sd 1·1) v. 2·7 (sd 1·53), P < 0·05) and had higher insulin sensitivity levels (12·6 (sd 3·8) v. 11·1 (sd 2·8) mg glucose/min per kg fat-free mass, P < 0·05). The present results suggest that the rate of weight loss during the first weeks of an intervention plays an important role in the completion of the programme. Thus, participants with low rates of initial weight loss should be monitored intensely to undertake corrective measures to increase the likelihood of completion.