Depending on the extent of the tumor, the treatment strategies for rectal cancer include primary surgical resection or, in the case of locally advanced carcinoma, neoadjuvant chemo(radio)therapy (C[R]Tx) or total neoadjuvant therapy (TNT), usually followed by surgical treatment. During resection, it is important to find a balance between radicality and preservation of function. Current data show that shorter safety margins are possible for patients who received neoadjuvant treatment without compromising the oncological outcome. This enables continence-preserving surgery in many patients with low rectal cancer. In these cases in particular, intraoperative frozen section diagnostics play a central role in confirming tumor-free margins. However, frozen section diagnostics also play an important role in the transanal resection of early carcinomas or in the therapy of recurrent rectal cancer. It should not be performed routinely, but rather in a targeted maner for specific questions and the corresponding therapeutic consequences. The informative value of frozen section diagnostics in neoadjuvant treated rectal cancer may be limited, so that the final assessment of the resection status and thus the determination of further therapy must be based on paraffin-embedded sections.