Biological-based (BbCAM) methods from complementary and alternative medicine (CAM) may interact with cancer treatments, reduce efficacy, or enhance adverse effects. Although CAM usage has been evaluated well in other cancer entities, data on melanoma patients are still missing. The aim of this study was to determine CAM usage of melanoma patients using a standardized questionnaire to identify potential interactions with established and new systemic melanoma therapies. This multicenter study was carried out in seven German skin cancer centers. During routine care contact, CAM usage of former and current melanoma treatment was assessed in melanoma patients. The probability of interaction was classified into four categories ranging from ‘interaction unlikely’ (I), ‘possible’ (II), ‘likely’ (III), or ‘no data’ (IV). The questionnaire was filled out by 1157 patients, of whom 1089 were eligible for evaluation. CAM usage was reported by 41% of melanoma patients, of whom 63.1% took BbCAM such as vitamins, trace elements, supplements, or phytotherapeuticals. Of 335 patients with former or current therapy, 28.1% used BbCAM. The melanoma treatment included interferon, radiotherapy, chemotherapy, BRAF-inhibitor, or other tyrosine kinase inhibitors and ipilimumab. On the basis of our model of likelihood of interaction, we found that 23.9% of those on cancer therapy and 85.1% of those also using BbCAM were at some risk of interactions. The main limitation of our study is that no reliable and comprehensive database on clinical relevant interactions with CAM in oncology exists. Most patients receiving a melanoma-specific treatment and using BbCAM methods are at risk for interactions, which raises concerns on the safety and treatment efficacy of these patients. To protect melanoma patients from potential harm by the combination of their cancer treatment and CAM usage, patients should systematically be encouraged to report their CAM use, while oncologists should be trained on evidence of CAM, and patient guidance for saver CAM use.