Introduction: The aim of this study was to develop a prototype of an anthroposophic complex intervention (CI) for oncological patients in primary care. Methods: Standardized methods for the development of CIs were used. Qualitative data were collected among professionals (n = 44) working in 3 Dutch anthroposophic primary care centers. The following topics were discussed in interviews and panel discussions (n = 12): treatment phases, treatment dimensions, treatment goals, and content of the indicated treatments and therapies. In a multidisciplinary focus group (n = 23) completeness and comprehensibility of the CI, and integration in daily practice were addressed. Subsequently, the developed CI was tested on face validity (n = 21) and compared with conventional guidelines. Results: Professionals reached consensus about 4 oncological treatment phases, 4 anthroposophic treatment dimensions, and twelve general treatment goals. The following anthroposophic therapies were found to be suited for oncological patients in primary care: medication (eg, mistletoe preparations); nursing (eg, external embrocation); physiotherapy (eg, rhythmic massage); eurythmy therapy; dietetics; art therapy; and counseling. The content of each therapy must be tailored to the individual. Comparison with existing guidelines demonstrated added value and the ability to fit with conventional care. Discussion: Strengths of the developed CI prototype are its focus on primary care, its practical applicability, the use of validated research methods, and the check on face validity in 2 other Dutch anthroposophic primary care centers. Limitations are that no systematic literature review was done and patient experiences were not collected. Conclusions: An applicable prototype of an anthroposophic CI for oncological patients in primary care was developed. To complete the development of this CI, a systematic review of the literature is needed, feasibility should be tested, patient experiences need to be collected, and implementation should be initiated and monitored. Finally, development of a patient decision aid (PtDA) and a decision-making tool (DMT) are recommended.