This article is the first part of a literature review concerning diabetic foot ulcers and the use of antimicrobial photodynamic therapy (PDT). Diabetic foot ulcers are associated with high morbidity, mortality, and healthcare costs. Natural healing is often delayed by microbial infection or colonisation, which might lead to serious complications, such as amputation. Furthermore, antibiotic treatment could have limited success because of the development of bacterial resistance and severely limited drug delivery to the ulcer due to vascular damage. PDT has antimicrobial effects and has been used to reduce the total and pathogenic microbial load in diabetic ulcers without inducing bacterial resistance. It is safe and can be used to improve outcomes. A clinical trial demonstrated that PDT with RLP068 reduced the microbial load of diabetic ulcers in 62 patients. This article reports previously published evidence and presents four, unpublished, clinical cases treated in the real-life setting.