Background: The inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC) are chronic, immune-mediated disorders of the digestive tract. IBD is considered to be a risk factor for developing osteoporosis; however current literature on this matter is inconsistent. Aim: To assess prevalence and development of osteoporosis and low bone mineral density (BMD), and its risk factors, in IBD patients. Methods: Systematic review of population-based studies. Studies were identified by electronic (January 2018) and manual searches (May 2018). Databases searched included EMBASE and PubMed and abstracts from 2014-2018 presented at the United European Gastroenterology Week, the European Crohn's and Colitis Organisation congress, and Digestive Disease Week were screened. Studies were eligible for inclusion if they investigated either the prevalence of osteoporosis or osteopenia and/or risk factors for osteoporosis or low BMD in IBD patients. Studies on children under the age of 18 were excluded. Only population-based studies were included. All risk factors for osteoporosis and low BMD investigated in any included article were considered. Study quality and the possibility of bias were analysed using the Newcastle-Ottawa scale. Results: Twelve studies including 3661 IBD patients and 12789 healthy controls were included. Prevalence of osteoporosis varied between 4%-9% in studies including both CD and UC patients; 2%-9% in studies including UC patients, and 7%-15% in studies including CD patients. Among healthy controls, prevalence of osteoporosis was 3% and 10% in two studies. CD diagnosis, lower body mass index (BMI), and lower body weight were risk factors associated with osteoporosis or low BMD. Findings regarding gender showed inconsistent results. CD patients had an increased risk for osteoporosis or low BMD over time, while UC patients did not. Increased age was associated with decreased BMD, and there was a positive association between weight and BMI and BMD over time. Great heterogeneity was found in the included studies in terms of study methodologies, definitions and the assessment of osteoporosis, and only a small number of population-based studies was available. Conclusion: This systematic review found a possible increase of prevalence of osteoporosis in CD cohorts when compared to UC and cohorts including both disease types. Lower weight and lower BMI were predictors of osteoporosis or low BMD in IBD patients. The results varied considerably between studies.