The anterior clinoid process (ACP) is usually removed during surgeries of proximal internal carotid artery (ICA) aneurysms. However, some ACPs present with air cells originating from the sphenoid or/and ethmoid sinus. In surgeries containing a clinoidectomy of a pneumatised process, up to 40% of patients experience cerebrospinal fluid (CSF) rhinorrhoea. The aim of this study was to explore the potential predictors of pneumatisation of the ACP, as well as to compare the occurrence of CSF rhinorrhoea between total and partial anterior clinoidectomies. This study comprised 2 different groups, with 2 different analyses. Firstly, the pneumatisation of the ACP was evaluated in 496 ACPs and was based on 248 computer tomography exams (CT). The c2 test and ROC curve comparisons were utilised in conjunction, to explore possible predictors of air cell accumulation in the ACP. The overall pneumatisation rate was 9.7%, unilateral and bilateral aerial ACP was found in 4.4% and 2.6% of all patients respectively, while at least one pneumatised ACP was found in 14.1% of examined patients. The route of pneumatisation was established in 87.5% of cases. The side of the ACP, gender, and patient age were not significantly associated with both pneumatisation of ACP or route of pneumatisation.Secondly, a clinical group of 23 patients after operative securing of an ICA aneurysm were retrospectively assessed with regards to the extent of anterior clinoidectomy and the occurrence of CSF rhinorrhoea. A total of 23 ACPs were removed, 17 ACPs were totally resected, and 6 underwent partial resection. CSF rhinorrhoea was not noted in any patients, thus the comparison between clinical groups was not valid. Moreover, we described a novel method of partial removal of the lateral aspect of ACP, which was applied in 6 patients treated for an ICA - ophthalmic artery junction aneurysm.