Various interpersonal factors have been considered in the understanding of hoarding disorder (HD), with three variables gaining particular attention: adult attachment, social support and loneliness. The review systematically evaluates evidence for these three variables, and how they may interrelate. Peer-reviewed studies and published dissertations that measured HD and one or more of the interpersonal factors via a validated measure were identified from EMBASE, MEDLINE, PsycINFO, PubMed and Scopus. Quality appraisal for each study was undertaken using a modified Downs and Black checklist. Twenty-six papers met inclusion criteria. The majority employed a cross-sectional design, in clinical and non-clinical samples. Fifteen studies examined attachment, showing that attachment style is relevant but not specific to hoarding disorder. Ten studies examined social support showing reduced social network with a specific difference in terms of perceived support in individuals with HD. Eight studies examined loneliness showing elevated loneliness in individuals with HD, again with some degree of specificity. Interpersonal factors are relevant to understanding HD with perceived support only showing evidence of being disorder specific. Further experimental and qualitative research is warranted to explore the nature and direction of these relationships, and how they may interrelate.