In the DSM IV-TR, Obsessive-Compulsive Disorder (OCD) is categorized as an anxiety disorder. A wide range of psychiatric and medical disorders, not included in this category, has been hypothesized to be related to OCD and to form a family of disorders known as obsessive compulsive spectrum disorders (OCSD). OCSD would include several clinically heterogeneous disorders such as Body Dysmorphic Disorder, Tourette's Syndrome or Pathological Gambling. This construct is based on disorders’ similarities with OCD in a variety of domains such as phenomenology, comorbidity, neurotransmitter or peptide systems, neurocircuitry, family history, genetic factors and treatment response. This presentation provides an overview of the existing literature regarding the concept of the OCD spectrum and the relationships between the disorders included in OCSD. Although there are data supporting the inclusion of some disorders in the OC spectrum, more research is needed to clarify the relationships and the boundaries between these disorders. Ultimately, a better understanding of OC spectrum may have significant implications for clinical practice.