BACKGROUND: Long-term recovery takes longer than expected despite improved surgical techniques and Enhanced Recovery After Surgery programs. An electronic health (eHealth) care program ("ikherstel") was developed to partially substitute perioperative care for patients undergoing colorectal surgical procedures. Successfully tested eHealth programs are not always implemented in usual care, and it is, therefore, important to evaluate the process to optimize future implementation. OBJECTIVE: The aim of this study was to evaluate whether the eHealth intervention was executed as planned. METHODS: A mixed-methods process evaluation was carried out alongside a multicenter randomized controlled trial (RCT). This evaluation was performed using the Linnan and Steckler framework for the quantitative part of this study, measuring the components reach, dose delivered, dose received, fidelity, and participants' attitudes. Total implementation scores were calculated using the averaging approach, in which the sum of all data points is divided by the number of data points and the total adherence to the protocol is measured. For the qualitative part, the Unified Theory of Acceptance and Use of Technology framework was used. The quantitative data were based on participants' questionnaires, a logistic database, a weblog, and participants' medical files and were obtained by performing semistructured interviews with participants of the RCT. RESULTS: A total of 151 participants of 340 eligible patients were included in the RCT, of which 73 participants were allocated to the intervention group. On the basis of the quantitative process data, total implementation scores for the website, mobile app, electronic consult, and activity tracker were 64%, 63%, 44%, and 67%, respectively. Participants in the qualitative part experienced the program as supportive and provided guidance on their recovery process after colorectal surgery. Most frequently mentioned barriers were the limited interaction with and feedback from health care professionals and the lack of tailoring of the convalescence plan in case of a different course of recovery. CONCLUSIONS: The intervention needs more interaction with and feedback from health care professionals and needs more tailored guidance in case of different recovery or treatment courses. To ensure a successful implementation of the program in daily practice, some adjustments are required to optimize the program in a blended care form. TRIAL REGISTRATION: Netherlands Trial Registry NTR5686; http://www.trialregister.nl/trialreg/admin/rctview.asp?TC= 5686 (Archieved by WebCite at http://www.webcitation.org/75LrJaHrr).