Complete tumor removal is one of the most important pillars within oncologic surgery. Tumor positive resection margins, where residual cancer tissue remains after surgery, drastically reduce survival. For surgeons, it is challenging to intraoperatively distinguish tumor tissue from healthy tissue in the margin, and there is no widely used imaging modality available that can aid for this problem. In this thesis we discuss fluorescence molecular imaging, an innovative technique where cancer tissue is fluorescently labeled and visualized intraoperatively. Here, the resection margin can be analyzed real-time during surgery for the presence of tumor tissue, and remaining cancer tissue can be removed in one setting. It has previously been shown that molecular fluorescence imaging can be applied intraoperatively in patients with squamous cell carcinoma of the oral cavity. However, we are the first to conduct a large study for this indication. We have shown the exquisite sensitivity of this technique, since all tumor positive margins can be detected. In addition, we have shown that fluorescence molecular imaging can be used to distinguish healthy tissue from cancerous tissue in patients with squamous cell carcinoma of the skin, and that it is possible to reliably detect lymph node metastases. We can conclude that molecular fluorescence imaging is a promising technique that can aid the surgeon intraoperatively for different indications. Larger studies should determine whether using this technique can also improve patient outcome, to justify the implementation of this technique in standard care.