Unprecedented obesity rates are changing the burden of disease worldwide and obesity-related health complications are increasing healthcare costs. In response, researchers, clinicians and public health practitioners are seeking new and effective tools such as the Internet to effect weight loss. This review highlights peer-reviewed literature on randomized controlled trials that examine Internet-delivered weight loss and maintenance programmes. The scope of this review is broader than previous reviews, including more males and non-Caucasian participants. The reviewed studies show intervention results ranging from no weight loss to an average loss of 7.6 kg. It is difficult to draw a definitive conclusion on the potential impact of Internet-based weight loss as study methods are highly variable between papers, low adherence was recorded and not all studies include a control group. As the demand for low-cost, efficacious interventions that yield statistically significant and/or clinically relevant results grows, more rigorous, population-specific research is needed to determine if Internet-delivered interventions may slow or reverse with weight gain and obesity and the associated health consequences.