The clinical course of ulcerative colitis (UC) may range from a quiescent course with prolonged periods of remission to fulminant disease requiring intensive medical treatment or surgery. Disease outcome is often determined by relapse rates, the development of colorectal cancer (CRC) and mortality rates. Early patient classification, identifying those with a high risk of developing complicated disease, is essential for choosing appropriate treatment. This paper reviews the clinical outcomes of UC patients as reported in population-based and observational studies representative of the whole patient population. Extensive colitis, a high level of systemic symptoms and young age at diagnosis are factors associated with a high risk of colectomy. Patients with distal disease who progress to extensive colitis seem to be a subgroup with an especially high risk of colectomy. Some prognostic factors of severe disease have been identified which could be used to optimize treatment and possibly reduce future complications. The overall risk of CRC and mortality was not significantly different from that of the background population. These results may have implications for follow-up strategies, especially regarding endoscopic surveillance of UC patients.