Purpose: To identify factors affecting length of stay (LOS) for adults participating in outpatient physical or occupational therapy programmes. Method: A scoping review of the literature was conducted using the Ovid MEDLINE, EMBASE, CINAHL, AMED, and Cochrane Library databases. Results: A total of 19 articles were retained from the search, and 2 additional articles were retrieved from grey literature (i.e., non-published sources). Personal factors affecting LOS are age and sex, both of which had inconsistent effects on LOS, and communication, language, physical, and cognitive difficulties, for which higher levels of function were generally associated with shorter LOS. Institutional factors affecting LOS were location, interdisciplinary communication, number of disciplines involved, and type of rehabilitation setting. Finally, two clinician-related factors—fewer treatment goals and a selection of evidence-informed treatment techniques—were associated with shorter LOS. Conclusions: Research on factors affecting adult outpatient rehabilitation LOS is limited and inconsistent. A preliminary list of LOS factors was produced, but this topic should be further explored with the collaboration of researchers and clinical institutions.