Objectives To determine whether an association exists between delirium and length of time indwelling urine catheters (IUC) are used in octogenarian patients treated with surgical aortic valve treatment (SAVR) or transcatheter aortic valve implantation (TAVI). Design Prospective cohort study. Setting Tertiary university hospital covering the western region of Norway. Participants Octogenarian patients undergoing elective SAVR or TAVI and willing to participate in the study were eligible. Patients unable to speak Norwegian were excluded. Between 2011 and 2013, 143 consecutive patients were included, and data from 136 of them are presented. Primary outcome Delirium. Results Logistic regression analysis shows that lower cognitive function was positively associated with delirium (OR 0.86, CI 0.74 to 0.99, p=0.047). Besides, the interaction term in the model shows that IUC use and delirium differed between SAVR and TAVI patients (p=0.04). The difference corresponded to a weaker association between hours of IUC use and delirium for SAVR (OR 1.01, CI: 0.99 to 1.03, p=0.54) compared with that for TAVI (OR 1.04, CI: 1.01 to 1.08, p=0.004). Conclusions The association between IUC use and delirium is stronger for octogenarian patients treated with TAVI than for patients who received SAVR. Our results revealed a previously unknown association between the number of hours an IUC is used and postoperative delirium in octogenarian patients treated with TAVI