It is unclear whether primary care physicians (PCPs) and nephrologists differ in their recognition of progressive chronic kidney disease (CKD), agree on diagnostic and referral strategies, and identify similar barriers to caring for patients. We conducted a national study of PCPs and nephrologists in the United States through a questionnaire describing a PCP caring for a patient with progressing CKD and questions to assess recognition of kidney dysfunction and approaches to diagnostic evaluation and referral. We identified participant and patient characteristics independently associated with CKD recognition and referral. We randomly identified a national sample of 304 physicians (126 nephrologists [39% response rate], 89 family physicians [28% response rate], and 89 general internists [28% response rate]). PCPs recognized CKD less (adjusted percentage, 59%; 95% confidence interval [CI], 47 to 69, family physicians; adjusted percentage, 78%; 95% CI, 67 to 86, general internists; adjusted percentage, 97%; 95% CI, 93 to 99, nephrologists; P < 0.01), differed from nephrologists in their recommendations for diagnostic testing, and recommended referral less (adjusted percentage, 76%; 95% CI, 65 to 84, family physicians; adjusted percentage, 81%; 95% CI, 70 to 89, general internists; adjusted percentage, 99%; 95% CI, 95 to 100, nephrologists; P < 0.01). PCPs differed from nephrologists in their expected intensity of specialists' involvement in care (16%, family physicians; 20%, general internists; 6%, nephrologists recommending nephrologist input monthly to every 6 months; P = 0.01). Lack of awareness of clinical practice guidelines and lack of clinical and administrative resources were identified as important barriers to care. PCPs recognize and recommend specialist care for progressive CKD less than nephrologists and differ in their clinical evaluations and expectations for referral. Improved dissemination of existing guidelines and targeted education in conjunction with efforts to build consensus among PCPs and nephrologists regarding their roles in the care of patients with CKD, including the collaborative development of clinical practice guidelines, could enhance patient care.