An unusual lipomatous tumour discovered accidentally in the right middle lobe of a 34-year old woman is described. The tumour was associated with an intrapulmonary typical chondromatous hamartoma in the same lobe but separate from the first lesion. The lipomatous tumour was primarily an intrapulmonary lipoma but in a few of the numerous sections made minute islands of cartilage and bone were discovered along with a few epithelial-lined clefts. These justify the diagnosis of a lipomatous hamartoma. Dispersed among the mature fat cells were a few immature cells with atypical nuclei. Cellular atypia in predominantly lipomatous hamartomas has not previously been reported. As the occurrence of atypical lipoblast-like cells might lead to an erroneous diagnosis of liposarcoma, this case is thought worthy of reporting.