More than a quarter of adults are now classified as obese and a further 42% of men and a third of women are overweight. The potentially preventable illness and premature death caused by obesity costs the NHS around £5.1 billion per year. Given the high prevalence of obesity there is a need to investigate the effectiveness of simple, cheap and pragmatic interventions that have the ability to be reach the high number of people needing to lose weight in the UK. Much of this management of obesity could potentially be initiated by GPs and primary care settings are the ideal place in which to intervene since most of the population can potentially be reached. Guidelines recommend that primary care physicians in England should identify people with obesity and offer clinical management, but few options for treatment exist in traditional primary care settings. Studies have shown GPs have a generally negative or ambivalent attitude to obesity management and they are seemingly reluctant to become involved. Studies have also reported GPs have a lack of confidence in the effectiveness of potential management options and limited time within a routine 10 min consultation to intervene. One potential option available to GPs that might address some of these issues is for GPs to refer their obese patients to widely available commercial weight management programmes (e.g. Slimming World and Weight Watchers) and in many areas in England the NHS offers these services free to patients and evidence supports the effectiveness of such provision. An alternative, potentially widely available, management option for obesity is for primary care teams to treat their obese patients themselves but recent evidence suggests they are ineffective and qualitative work has indicated that patients would prefer support from external agencies anyway. We conducted the Lighten Up trial (Jolly et al 2011, BMJ) where we investigated the effectiveness of several pragmatic interventions in 740 obese or overweight adults with a co-morbid disorder identified from general practice records. Participants were randomised to entitlement to free commercial weight loss management programmes (Weight Watchers, Slimming World or Rosemary Conley), primary care management (general practice or pharmacy support), a choice of any programme and a minimal intervention comparator group for 12 weeks. All programmes achieved significant weight loss from baseline to programme end at 12 weeks follow up (range 1.37 kg (general practice) to 4.43 kg (Weight Watchers)), and all except general practice and pharmacy provision resulted in significant weight loss at one year. At one year, only the Weight Watchers group had significantly greater weight loss than the comparator group with 2.5 kg greater loss. Collectively the commercial programmes achieved significantly greater weight loss than did the primary care interventions at programme end (mean difference 2.3 kg). The primary care programmes were the most costly to provide. The results of the Lighten Up trial are similar to those of the trial by Jebb and colleagues (Lancet 2011) where 772 participants randomised to 12 months Weight Watchers or GP care achieved a weight loss of 4.0 kg and 1.6 kg respectively at 1 year follow up. Evidence indicates that commercially provided weight management services are more effective and cheaper than primary care based services, which are ineffective and not popular with patients. However, the vast majority of people who lose weight will regain this weight within 1-2 years therefore it is critical that effective interventions are also available to ensure weight loss is maintained over the longer term.