Primary care physicians provide care to a disproportionate number of overweight and obese patients and are uniquely positioned to help patients manage their weight in the context of a continuity relationship. The US National Heart, Lung and Blood Institute (NHLBI) developed evidence-based guidelines for the effective and efficient care of overweight/obese patients, but little is known about the use of these guidelines in practice. To determine the content of weight discussions and assess the elements of the NHLBI guidelines that were accomplished, office visits of 544 adult, overweight/obese patients to 28 primary care physicians were observed and audio recorded. Associations between type of weight management discussion and patient, physician and visit characteristics were examined. Fifty per cent (n = 270) of visits included weight discussions; 47% and 38% included use of at least one NHLBI assessment or treatment element during discussions about weight, respectively. Only 35% (n = 193) of discussions included an assessment and treatment strategy; none included all NHLBI-recommended elements. Overall, adherence to guidelines was poor, particularly with regard to reporting body mass index to the patient, measuring waist circumference and setting realistic weight loss goals. Weight discussions did not clearly vary by the patient, physician or visit characteristics examined. These findings suggest opportunities to develop and further tailor resources for improved physician training in patient weight management communication and treatment techniques that are both consistent with current standards for effective, evidence-based care and efficient enough for routine use during busy primary care visits.