Despite the perennial popularity of readmission as an indicator of the quality of hospital care, the empiric evidence linking it to process-of-care problems during the prior hospitalization is inconsistent. We devised a conceptual model for the use of unscheduled readmission within 31 days as an indicator of the quality of medical-surgical inpatient care for adults, and then conducted a systematic review of the readmission literature to determine the extent to which the evidence supports the proposed relationships. A fairly complex web of relationships influences the association between the process of inpatient care and early readmission. From the evidence to date, it is impossible to say with confidence that early readmission is or is not a valid and useful quality indicator. In most negative studies, the absence of an association appears to be explainable on the basis of improper study design, omission of important variables, or mis-specification of variables. Variables intervening between or confounding the relationship of the process of inpatient care to early readmission have received inadequate attention in past work. Investigators can use the proposed model and literature review to ensure their work advances the field and puts the hypothesis that early readmission is a valid quality indicator to a rigorous test. This matter has a certain urgency in view of the vast amount of resources that providers and payers devote to monitoring readmission rates and reviewing readmissions.