Osteochondroma is the most common benign bone tumour. The risk of sarcomatous change in an isolated lesion is approximately 1%. We report a case of an isolated osteochondroma which appeared benign on clinical and plain radiographic examination but routine histological analysis revealed non-Hodgkin’s lymphoma in the underlying bone. This association has not previously been reported and the case emphasises the importance of routine histological analysis, even if a lesion appears benign.