INTRODUCTION: In the context of the development of pharmaceutical interventions, expectations and experiences of participants are essential. Their insights may be particularly helpful to address the challenges of recruiting and retaining participants for Alzheimer's disease (AD) clinical trials. We examined clinical trial participants' experiences to optimize trial design in Alzheimer's disease (AD). METHOD: In this mixed-methods study, we included adults who participated in sponsor-initiated AD trials at Brain Research Center, a clinical trial organization in the Netherlands. Participants (N = 71, age 69 ± 6.5, 54%F, 19 cognitively normal (CN), 19 mild cognitive impairment (MCI), and 33 AD dementia) first completed an online survey. Diagnostic group differences were investigated using chi-square tests or one-way ANOVAs. Next, a subsample (N = 12; 8 = CN, 4 = MCI) participated in focus groups to gain in-depth insight into their opinions on optimizing trial design from a participants' point of view. Audio recordings from focus group interviews were transcribed verbatim and analyzed by thematic content analysis by two independent researchers. RESULTS: Most reported motives for enrolment included "to benefit future generations" (89%), followed by "for science" (66%) and "better monitoring" (42%). Frequent suggestions for increasing willingness to participate included a smaller chance to receive placebo (n = 38, 54%), shorter travel times (n = 27, 38%), and sharing individual results of different assessments (n = 57, 80%), as well as receiving trial results (n = 52, 73). Highest visual analogue burden scores (0-100) were found for the lumbar puncture (M = 47.2, SD = 38.2) and cognitive assessments (M = 27.2, SD = 25.7). Results did not differ between diagnostic groups, nor between patient and caregiver participants (all p-values>.05). Two additional themes emerged from the focus groups: "trial design," such as follow-up visit(s) after participating, and "trial center," including the relevance of a professional ...