Schizoid personality disorder (ScPD) is one of the "odd cluster" or "cluster A" personality disorders in DSM-IV. In the present article, the authors review information pertaining to the psychometric characteristics of ScPD as gleaned from a search of relevant publications as well as from databases of personality disorder study groups. Comparatively little evidence exists for the validity and reliability of ScPD as a separate, multifaceted personality disorder. Some authors, moreover, have contended that the group of patients termed "schizoid" actually fall into two distinct groups--an "affect constricted" group, who might better be subsumed within schizotypal personality disorder, and a "seclusive" group, who might better be subsumed within avoidant personality disorder. The research-based justification for retaining ScPD as an independent diagnosis is sufficiently sparse for it to seem reasonable to remove ScPD from the list of personality disorders in DSM-V, and instead to invite clinicians to code for schizoid traits using a dimensional model.