BACKGROUND AND OBJECTIVES: Collaboration between primary care physicians (PCPs) and nephrologists in the care of patients with chronic kidney disease (CKD) is widely advocated, but physician preferences regarding collaboration are unknown. Physicians' desires to collaborate in the care of a hypothetical patient with CKD, their preferred content of collaboration, and their perceived barriers to collaboration were assessed. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A questionnaire describing the care of a hypothetical patient with progressive CKD was administered to a national sample of U.S. PCPs and nephrologists. Physician characteristics and attitudes associated with desires to collaborate were identified. RESULTS: Among 124 PCPs and 120 nephrologists, most physicians (85% PCPs versus 94% nephrologists) desired collaboration. Nephrologists were more likely than PCPs to prefer collaboration focus on predialysis/renal replacement therapy preparation and electrolyte management (73% versus 52% and 81% versus 46%, respectively). PCPs were more likely to desire collaboration if the hypothetical patient had diabetes and hypertension (versus hypertension alone), if they believed the care they provide helps slow CKD disease progression, and if they did not perceive health insurance as a barrier to nephrology referral (adjusted percentages [95% confidence interval]: 94% [80 to 98] versus 75% [reference]), 92% [75 to 98] versus 75% [reference], 42% [9 to 85] versus 88% [reference], respectively). CONCLUSIONS: Most PCPs and nephrologists favored collaborative care for a patient with progressive CKD, but their preferred content of collaboration differed. Collaborative models that explicitly include PCPs in the care of patients with CKD may help improve patients' clinical outcomes.