We aimed to evaluate the impact of knee periprosthetic joint infection (PJI) by assessing the patients' long-term quality of life and explicitly their psychological wellbeing after successful treatment. Thirty-six patients with achieved eradication of infection after knee PJI were included. Quality of life was evaluated with the EQ-5D and SF-36 outcome instruments as well as with an ICD-10 based symptom rating (ISR) and compared to normative data. At a follow-up of 4.9 ± 3.5 years the mean SF-36 score was 24.82 ± 10.0 regarding the physical health component and 46.16 ± 13.3 regarding the mental health component compared to German normative values of 48.36 ± 9.4 ( < 0.001) and 50.87 ± 8.8 ( = 0.003). The mean EQ-5D index reached 0.55 ± 0.33 with an EQ-5D VAS rating of 52.14 ± 19.9 compared to reference scores of 0.891 ( < 0.001) and 68.6 ± 1.1 ( < 0.001). Mean scores of the ISR revealed the psychological symptom burden on the depression scale. PJI patients still suffer from significantly lower quality of life compared to normative data, even years after surgically successful treatment. Future clinical studies should focus on patient-related outcome measures. Newly emerging treatment strategies, prevention methods, and interdisciplinary approaches should be implemented to improve the quality of life of PJI patients.