A better understanding of the association between early physician follow-up after discharge and adverse outcomes among hospitalized patients may inform interventions aimed at reducing readmission for common chronic conditions. To assess whether hospitalized patients with early physician follow-up after discharge had lower rates of overall and condition-specific readmissions within 30 days and 90 days of discharge. This cohort study was conducted among Ontario, Canada, adults with first admission for acute myocardial infarction (AMI), congestive heart failure (CHF), or chronic obstructive pulmonary disease (COPD) during 2005 to 2019. The exposure was follow-up visit with a primary care physician or relevant specialist within 7 days of discharge. Cox proportional hazards models were used to compare patients with vs without early follow-up, adjusting for sociodemographic factors and comorbidities, weighting by propensity score-based overlap weights. Data were analyzed from January through July 2021. Primary outcomes were 30-day and 90-day readmissions, cardiac readmissions (readmission for AMI, CHF, or angina) for patients with cardiac conditions, and COPD-related readmissions for patients with COPD. Mortality at 30 days and 90 days was a secondary outcome. All percentages reported in Results are unweighted. The study cohort comprised 450 746 patients, including 198 854 patients with AMI, 133 058 patients with CHF, and 118 834 patients with COPD; the median (IQR) age was 66 (56-77) years for AMI, 78 (68-85) years for CHF, and 73 (64-81) years for COPD, and there were 64 339 (32.35%) women, 62 575 (47.03%) women, and 59 179 (49.80%) women, respectively. There were 91 182 patients (45.85%), 56 491 patients (42.46%), and 40 159 patients (33.79%), respectively, who received an early follow-up visit. Overall, patients with early follow-up had higher rates of collaborative care (eg, CHF: 20 931 patients [37.85%] vs 11 101 of 76 567 patients [14.85%]) and visits to a specialist within 30 days (eg, CHF: 25 797 patients [45.67%] vs 20 548 patients [26.84%]). Those with early follow-up had lower 90-day readmission rates among patients with CHF (15 934 patients [28.21%] vs 23 121 patients [30.20%]; adjusted hazard ratio [aHR], 0.98; 95% CI, 0.96-0.99) and among those with COPD (8784 patients [21.87%] vs 18 097 of 78 675 patients [23.00%]; aHR, 0.95; 95% CI, 0.93-0.98). Among patients with COPD, those with early follow-up had lower 90-day COPD-related readmission rates (4015 patients [10.00%] vs 8449 patients [10.74%]; aHR, 0.93; 95% CI, 0.89-0.96), and among patients with CHF, those with early follow-up had lower 90-day mortality rates (4044 patients [7.16%] vs 6281 patients [8.20%]; aHR, 0.93; 95% CI, 0.90-0.97). There were no significant benefits at 30 days or for patients with AMI. These findings suggest that early follow-up in conjunction with a comprehensive transitional care strategy for hospitalized patients with medically complex conditions coupled with ongoing effective chronic disease management may be associated with reduced 90-day readmissions.