Despite modern therapies, the 5-year survival of patients with an intraoral squamous cell carcinoma (PECA) remains poor at 50%. The most important prognostic factors are the tumour size and the presence of lymph node metastases (CM) at the time of initial diagnosis and the development of a relapse during the follow-up. With regard to the relapse behavior, there are few data, making early detection in tumour aftercare extremely difficult. This is also reflected in a low level of evidence for the approach in tumour aftercare in the German guideline. Retrospectively, over the years 2000-2014, the oral and maxillofacial surgery patients at the University Medical Center Mainz who developed a primary intraoral PECA and were treated in domo were re-examined. In addition to studying the epidemiological data, the risk factors and the TNM-status, the focus was on the relapse behaviour and types as well as the influencing factors and the diagnosis. Overall, 766 patients (34% women and 66% men) were compared at a mean age of 62 ± 13 years. Due to the high number of T3-4 tumours (33%) and the high rate of lymph node metastases (37%), 50% of patients already had an advanced tumour stage (III-IV). Here, 70% developed a relapse within the first 2 years, with a median of 12 months within the examined group of people. The most common type of relapse was a local recurrence, with 36%. 55% of the relapses were diagnosed using a clinical investigation method. The presence of poorly differentiated tumours and the existence of lymph node metastasis were statistically significantly more often accompanied by the development of a recurrence. An advanced tumor stage, the presence of lymph node metastasis, and relapses are typically associated with a worse 10-year survival. Thus it can be concluded that intraoral PECA recurs particularly often in the presence of cervical metastases and an undifferentiated tumour . These data reinforce the absolute necessity of a close-knit clinical follow-up, especially during the first 2 years, which should go beyond the recommended guidelines in a three-month rhythm to detect the relapse in a timely manner. Keywords: Oral squamous cell carcinomas, relapse behaviour, relapse diagnosis, recall, follow-up