Obsessive-compulsive disorder is a very heterogeneous condition, not always easy to be identified. Obsessions are intrusive thoughts, impulses or images that cause anxiety or other emotional discomfort, whereas compulsions are repetitive behaviors or mental acts voluntarily performed to counterbalance or minimize the discomfort, or magically prevent any feared events. The most common symptoms are contamination, aggressive, somatic and sexual obsessions and washing, checking, repeating, counting and ordering compulsions. Patients usually have multiple symptoms simultaneously, which often change over time. Although the insight is typically preserved, it varies among patients and also fluctuates in the same patient in different ocasions. The main features are: exacerbated appraisal of risks, pathological doubts and incompleteness, as well as excessive sense of responsibility and guilt and thought/action fusion. As patients frequently feel ashamed of their symptoms, they can be reticent about them. Consequently, it usually takes time till they get adequate treatment.