Objectives: This retrospective study aimed to assess the performance of posterior composite resin restorations (PCRRs) and evaluate the influence of patient-specific factors on restoration outcomes. Methods: A total of 189 PCRRs were examined in 54 patients, with evaluations based on Modified USPHS criteria. Patient-specific factors were analyzed. Statistical analyses, including chi-square tests, independent samples t-tests, and ANOVA tests, were conducted. Results: Patients aged over 50 exhibited higher DMFT averages and a higher rate of unsuccessful restorations. Despite higher DMFT scores in females, gender doesn't significantly impact restoration outcomes. Secondary caries correlated with. plaque scores, significantly affecting restoration survival. Marginal adaptation, retention deficiencies, and secondary caries were primary causes of failure. Multi-surface restorations faced higher failure risk due to elevated plaque scores. Class-V restorations showed a higher failure rate, challenging the number of surfaces and longevity correlation. Conclusions: This study identified key factors influencing posterior composite resin restorations-(PCRRs) in patients over 50, including higher DMFT averages and more unsuccessful restorations. No significant difference was found between brushing; frequency and DMFT rates, possibly due to the absence of non-brushers. Secondary caries; correlated with elevated plaque scores, impacting restoration survival. Primary causes of; failure included marginal adaptation issues, retention deficiencies, and secondary caries, with multi-surface restorations facing a higher risk. However, tooth vitality, beverage and acidic food consumption, and oral hygiene habits did not significantly affect PCRR outcomes. Clinical significance: Patient-specific factors significantly impact PCRRs' long-term performance. Dentists must tailor strategies, emphasizing regular monitoring and preventive measures for extended survival.