Background Despite similar clinical symptoms, collagenous colitis (CC) and lymphocytic colitis (LC) are considered two distinct disease entities. Aim To compare pathoanatomical findings, clinical presentations, risk factors, course of diseases and response to treatment in CC and LC to establish whether they could be subtypes of the same disease, microscopic colitis (MC). Methods The MEDLINE was searched for CC, LC and MC, and clinical studies of >20 patients were included. Pooled results with 95% confidence intervals were calculated based on the number of patients. Results An abnormal number of intraepithelial lymphocytes are found in 45% (40-50%) with CC, and an abnormal subepithelial collagen band in 16% (13-20%) with LC suggesting a histological overlap. The incidence of CC and LC has increased in parallel. Mean age (CC 63 years; LC 60 years) and clinical presentation are indistinguishable, and females are predominant in CC (77%; 75-79%) as well as LC (68%; 66-70%). Risk factors such as nonsteroid anti-inflammatory drugs consumption CC 39% (36-42%); LC 32% (29-35%) are similar and prevalence of concomitant autoimmune diseases such as coeliac disease (CC 5%; CI: 4-6% and LC 7%; CI: 6-9%) do not differ. Bile acid diarrhoea is highly prevalent in CC (41%; 37-45%) and LC (29%; 24-34%). The effect of budesonide is identical. Conclusions CC and LC could be considered histological subtypes of the same disease, MC. To facilitate recruitment to clinical trials, all MC patients could be included in future trials and stratified for subtypes.