This paper presents a safety reporting smartphone application which is expected to reduce the occurrence of postoperative adverse events after total hip arthroplasty (THA). A user-centered design approach was utilized to facilitate optimal user experience. Two main implemented functionalities capture patient pain levels and well-being, the two dimensions of patient status that are intuitive and commonly checked. For these and other functionalities, mobile technology could enable timely safety reporting and collection of patient data out of a hospital setting. The HCI expert, and healthcare professionals from the Haukeland University Hospital in Bergen have assessed the design with respect to the interaction flow, information content, and self-reporting functionalities. They have found it to be practical, intuitive, sufficient and simple for users. Patient self-reporting could help recognizing safety issues and adverse events.