Objective To describe how often PICCs are retained when not needed (no medical indication, "idle") in adult patients and to analyze the associated factors. Methods A retrospective observational study was conducted of 358 adult patients with PICCs from 5 tertiary hospitals in Shanghai. Results PICCs of 255 patients (71.2%) were idle. Logistic regression analysis showed that interpersonal communication, self-reported influence of PICCs, medical payment type, chemotherapy courses, insertion arms and persons who advised PICC removal were predictive factors (P<0.05, P<0.01). Conclusion Most PICCs that are not needed were not promptly removed, so measures targeted to the risk factors should be taken to reduce "idle PICC-days" and facilitate the appropriate use of PICC.