Transmural healing is associated with substantial improvements in disease-related outcomes for patients with Crohn's disease, but there is no single validated definition of transmural healing to date. We did a systematic review to summarise the available definitions and to evaluate the effect of transmural healing on disease-related outcomes for patients with Crohn's disease by searching PubMed, Cochrane Library, and Web of Science for interventional and non-interventional studies. Seventeen studies were included, reporting rates of transmural healing in between 14·0% and 42·4% of patients. Transmural healing was assessed with magnetic resonance enterography, bowel sonography, or CT enterography. Most studies used bowel wall thickness, with 3 mm or less as the most frequent cutoff, to define transmural healing. Vascularisation assessed by doppler ultrasound and absence of complications or contrast enhancement were also used for this definition. Transmural healing was significantly associated with improvements in disease-related outcomes. In addition, there was a good correlation between transmural healing, mucosal healing, and selected biomarkers. We conclude that bowel wall thickness is the most frequently used item to evaluate transmural healing, which is associated with improvements in long-term outcomes of Crohn's disease and should be considered as a new treatment target.