Collaborative Care refers to a partnership between healthcare professionals and patients who feel confident to manage their health conditions. Using an Internet-based assessment of health needs and healthcare quality, we surveyed 24,609 adult Americans aged 19 to 69 who had common chronic diseases or significant dysfunction. In these patients, we examined the association of Collaborative Care with specific measures for treatment effect, disease control, prevention, and economic impacts. These measures were adjusted for respondents' demographic characteristics, burden of illness, health behaviors, and overall quality of healthcare. Only 21% of respondents participated in good Collaborative Care, 36% attained fair Collaborative Care, and 43% experienced poor Collaborative Care. Regardless of overall care quality or the respondents' personal characteristics, burden of illness, or health behaviors, good Collaborative Care was associated with better control of blood pressure, blood glucose level, serum cholesterol level, and treatment effectiveness for pain and emotional problems. Some preventive actions were better, and some adverse economic impacts of illness were mitigated.