Melanotic hyperpigmentation of the mucosa secondary to radiotherapy is a rare occurrence. It is a diagnosis of exclusion. Literature review has identified only two case reports published to date. We present a case of a patient treated at our institution. An 18-year-old male patient of Nigerian descent underwent radical radiotherapy (36 Gy in 18 daily fractions) to his right neck for paediatric type follicular lymphoma over a period of four weeks. He developed hyperpigmented tongue lesions during the third week of radiotherapy. There was no associated tongue discomfort, inflammation, infection, or pigmentation change elsewhere in the oral mucosa. Review of medications and past medical history did not demonstrate any potential contributing factors. Full blood count and biochemistry, morning cortisol levels and coagulation screen were all normal apart from mild neutropenia and lymphopenia. His oral cavity received a mean dose of 16.4 Gy, with the right side of his tongue receiving up to 37.5 Gy as this was within the planning target volume (PTV). He had an excellent response to radiotherapy and remains in remission. The tongue lesions resolved spontaneously 3 months post treatment.