Sir, With the ever-increasing use of imaging, the finding of intracranial fat is a common occurrence. We have noted several cases of intracranial fat deposits being found in our routine clinical practice. These have occurred in patients who were being investigated for unrelated reasons and where the finding was purely an incidental one. We have recently found an unusual case of a large intracranial fat deposit occurring in the straight sinus (Figs. 1 and 2). Therefore, we would like to review the literature on this topic with a discussion of the differential diagnosis of intracranial fat, which we hope may prove useful when reporting such findings. Most deposits of intracranial fat are asymptomatic. In fact, prior to the introduction of CT and MRI, these lesions were only found incidentally at autopsies conducted for unrelated causes. Fat within the cranium is often presumed to indicate the presence of a fat-containing tumor such as a lipoma, dermoid cyst, epidermoid cyst or teratoma. In particular, deposits with the signal characteristics of simple fat are often assumed to be lipomas. However, such tumors are, in fact, rare. Lipomas account for less than 0.1% of all intracranial tumors. In 1975, New and Scott were the first to diagnose intracranial lipoma using CT [1, 2]. Then, in 1985, Kean demonstrated the first lipoma using MRI [1, 2]. Several hundred cases of intracranial lipomas have subsequently been reported in the world literature. Characteristically, the appearance of an intracranial lipoma on CT is that of a well-demarcated hypodense lesion, with a density typically of between −10HU and −100HU [3]. They may also have a calcified fibrous capsule and do not usually enhance after contrast [4]. There is no generally accepted theory of the development of intracranial lipomas. They are now predominantly accepted, not to be true tumors, but to be congenital anomalies, resulting from the abnormal persistence and mall differentiation of the menix primitiva, the mesenchymal anlage of the meninges [5]. They are found mainly in the midline and are often associated with other development anomalies. Over 50% of the cases are described to occur in the region of the corpus callosum. Other sites include the quadreminal cistern, ambient cistern, cerebello-pontine angle and pineal gland [6]. Furthermore, new sites of intracranial lipomas continue to be reported. Neuroradiology (2009) 51:787–788 DOI 10.1007/s00234-009-0547-2