Background: Economic evaluations are less commonly applied to implementation interventions compared to clinical interventions. The efficacy of an implementation strategy to improve adherence to screening guidelines among first-degree relatives of people with colorectal cancer was recently evaluated in a randomized-controlled trial. Using these trial data, we examined the costs and cost-effectiveness of the intervention from societal and health care funder perspectives. Method: In this prospective, trial-based evaluation, mean costs, and outcomes were calculated. The primary outcome of the trial was the proportion of participants who had screening tests in the year following the intervention commensurate with their risk category. Quality-adjusted life years were included as secondary outcomes. Intervention costs were determined from trial records. Standard Australian unit costs for 2016/2017 were applied. Cost-effectiveness was assessed using the net benefit framework. Nonparametric bootstrapping was used to calculate uncertainty intervals (UIs) around the costs and the incremental net monetary benefit statistic. Results: Compared with usual care, mean health sector costs were $17 (95% UI [$14, $24]) higher for those receiving the intervention. The incremental cost-effectiveness ratio for the primary trial outcome was calculated to be $258 (95% UI [$184, $441]) per additional person appropriately screened. The significant difference in adherence to screening guidelines between the usual care and intervention groups did not translate into a mean quality-adjusted life year difference. Discussion: Providing information on both the costs and outcomes of implementation interventions is important to inform public health care investment decisions. Challenges in the application of cost-utility analysis hampered the interpretation of results and potentially underestimated the value of the intervention. Further research in the form of a modeled extrapolation of the intermediate increased adherence effect and distributional cost-effectiveness to include equity requirements is warranted.