Obsessive-compulsive disorder (OCD) is a condition where sufferers experience unwelcome thoughts that repeatedly intrude into their mind (obsessions) and/or repeated unwelcome urges to perform certain actions (compulsions). In both cases, the sufferer has little or no control over these unwelcome thoughts and urges.
Typically, obsessions may involve fears or anxieties about issues such as hygiene (eg. dirt, contamination, germs etc) or safety (eg. door locks, light and power switches, gas controls etc), although other issues such as sexual thoughts, blasphemous thoughts and the symmetrical placement of objects may also form the subject matter of obsessions.
Compulsions may also related to similar issues, and may involve repetitive hand-washing, cleaning, checking (eg. of light switches, locks etc), counting, touching and arranging.