The effect of a greater volume of patients with similar conditions being treated at a hospital on the outcomes achieved is investigated for almost 500,000 selected surgical and medical patients treated in over 1,200 nonfederal United States hospitals. In Part I the authors found strong and consistent evidence for surgical patients that high volume is associated with better outcome; evidence for medical patients was mixed. In this paper the authors include other hospital variables related both to volume and outcome—hospital size, teaching status, and expenditures—to determine whether they mask the true relationship; still, strong and consistent evidence that greater volume produces better outcome was found for both surgical and medical patients. This relation was significant for low-, medium-, and high-risk patients. Among the hospital variations added, only size was consistently and strongly related to outcome; greater size was associated with poorer outcome after accounting for volume. The potential importance of the findings for reducing deaths and days in hospital on a national level is discussed. The evidence is strongly supportive of the need for policies that would promote greater regionalization of a given service, and not greater size, to obtain better quality outcome for patients treated.