Background: Factors predictive of the efficacy of pelvic floor muscle training (PFMT) in stress urinary incontinence (SUI) or mixed urinary incontinence (MUI) are poorly defined. Identifying these factors is crucial for guiding treatment decisions, determining training repetitions, and predicting PFMT outcomes. Objective: This study aimed to identify clinical factors predictive of PFMT outcomes in women with primary SUI. Methods: We retrospectively reviewed data from 188 consecutive women with either SUI (n = 90) or MUI (n = 98) with a primary stress component. All participants underwent a 3-month PFMT program. Predictive factors for 50% improvement and complete cure of incontinence were assessed through urogynecological history/examination, medical history, digital pelvic floor muscle (PFM) evaluation (n = 87), and 3-day bladder diaries. Logistic regression analyses were conducted for the overall group and separately for the SUI and MUI subpopulations. Results: At 3 months, 10% of SUI patients and 11.2% of MUI patients achieved complete SUI cure, while 35.7% of MUI patients were free from urge urinary incontinence (UUI). A complete cure of SUI was correlated with a negative or mildly positive results of stress test (p = 0.014). For MUI patients, complete UUI cure was linked to initial digital PFM evaluation results (p = 0.003) and negative (p = 0.005) or mildly positive findings of stress tests (p = 0.003). The absence of prior surgery and digital evaluation predicted a 50% improvement in MUI (p = 0.021 and p = 0.026, respectively). Endurance improvement was related independently with >50% improvement in MUI patients (odds ratio = 3.794, p = 0.019). Conclusion: Negative or mildly positive stress tests and digital PFM evaluation predict better outcomes with PFMT. Further prospective studies are needed to validate these findings.