BACKGROUND The transition between the inpatient and outpatient setting is a high-risk period for patients. The presence and role of the primary care provider (PCP) is critical during this transition. This study evaluated characteristics and outcomes of discharged patients lacking timely PCP follow-up, defined as within 4 weeks of discharge. METHODS This prospective cohort enrolled 65 patients admitted to University of Colorado Hospital, an urban 425-bed tertiary care center. We collected patient demographics, diagnosis, payer source and PCP information. Post-discharge phone calls determined PCP follow-up and readmission status. Thirty-day readmission rate and hospital length of stay (LOS) were compared in patients with and without timely PCP follow-up. RESULTS The rate of timely PCP follow-up was 49%. For a patient’s same medical condition, the 30-day readmission rate was 12%. Patients lacking timely PCP follow-up were 10 times more likely to be readmitted (odds ratio [OR] = 9.9, P = 0.04): 21% in patients lacking timely PCP follow-up vs. 3% in patients with timely PCP follow-up, P = 0.03. Lack of insurance was associated with lower rates of timely PCP follow-up: 29% vs. 56% (P = 0.06), but did not independently increase readmission rate or LOS (OR = 1.0, P = 0.96). Index hospital LOS was longer in patients lacking timely PCP follow-up: 4.4 days vs. 6.3 days, P = 0.11. CONCLUSIONS Many patients discharged from this large urban academic hospital lacked timely outpatient PCP follow-up resulting in higher rates of readmission and a non-significant trend toward longer hospital LOS. Effective transitioning of care for vulnerable patients may require timely PCP follow-up.