Four patients with colitis, in two of whom the etiology was unknown, are presented. One patient with discontinuous segmental colitis was infected by Aeromonas hydrophila, and another with presumed idiopathic inflammatory bowel disease was superinfected by this pathogen. Although Aeromonas hydrophila has been known as a rare cause of diarrhea in our region, it is in the first instance reported to cause severe long-lasting colitis as well as superinfection of idiopathic inflammatory bowel disease (IIBD). Another patient presented with segmental ischemic colitis which was rather atypical and of unknown etiology; the patient was young and had no predisposing factors for vascular occlusive disease. The fourth patient with long-lasting segmental granulomatous colitis which was suspected to be parasitic in origin remained without a definitive diagnosis. This presentation of patients with endoscopically proven colitis should in view of our increasing knowledge of colitis remind us to keep a look out for new infections and other forms of inflammatory bowel disease.