Objective: This study investigated predictors of progression of coronary atherosclerosis after percutaneous coronary intervention. Their identification may be useful in clinical practice. Methods: We retrospectively reviewed the database of the Cardiology Department of the Cardiovascular Disease and Heart Transplant Institute in Tirgu Mures from January 2012 to December 2015 and identified 180 patients readmitted after successful percutaneous coronary intervention. The t-test, chi-square test, Fisher’s exact test, and mono- and multivariate analyses were used to evaluate associations between the patients’ clinical and angiographic characteristics and the progression of coronary atherosclerosis. Results: The pre-percutaneous coronary intervention atherosclerotic burden was associated with a higher number of new coronary lesions at readmission. Hypertension and the placement of more than one bare-metal stent in the right coronary artery were associated with increased odds of the progression of coronary atherosclerosis. The use of drug-eluting stents at the index percutaneous coronary intervention and a greater number of drug-eluting stents in the left anterior descending artery were associated with a decreased chance of the progression of coronary atherosclerosis. Conclusions: A massive atherosclerotic load at index percutaneous coronary intervention and hypertension were predictors of the progression of coronary artery atherosclerosis. The number, type, and localisation of the stent at the index percutaneous intervention could influence the progression of coronary atherosclerosis. Further research is needed to identify other potential predictors and to determine how to optimize the treatment of known predictors.