Background: Survivors of childhood cancer are at risk of subsequent primary malignant neoplasms (SPNs), but the risk for rarer types of SPNs, such as oral cancer, is uncertain. Previous studies included few oral SPNs, hence large-scale cohorts are required to identify groups at risks. Methods: The PanCareSurFup cohort includes 69,460 5-year survivors of childhood cancer across Europe. Risks of oral SPNs were defined by standardised incidence ratios (SIRs), absolute excess risks and cumulative incidence. Results: One hundred and forty-five oral SPNs (64 salivary gland, 38 tongue, 20 pharynx, 2 lip, and 21 other) were ascertained among 143 survivors. Survivors were at 5-fold risk of an oral SPN (95% CI: 4.4–5.6). Survivors of leukaemia were at greatest risk (SIR = 19.2; 95% CI: 14.6–25.2) followed by bone sarcoma (SIR = 6.4, 95% CI: 3.7–11.0), Hodgkin lymphoma (SIR = 6.2, 95% CI: 3.9–9.9) and soft-tissue sarcoma (SIR = 5.0, 95% CI: 3.0–8.5). Survivors treated with radiotherapy were at 33-fold risk of salivary gland SPNs (95% CI: 25.3–44.5), particularly Hodgkin lymphoma (SIR = 66.2, 95% CI: 43.6–100.5) and leukaemia (SIR = 50.5, 95% CI: 36.1–70.7) survivors. Survivors treated with chemotherapy had a substantially increased risk of a tongue SPN (SIR = 15.9, 95% CI: 10.6–23.7). Conclusions: Previous radiotherapy increases the risk of salivary gland SPNs considerably, while chemotherapy increases the risk of tongue SPNs substantially. Awareness of these risks among both health-care professionals and survivors could play a crucial role in detecting oral SPNs early.