Objectives Inappropriate use of mannitol is a medical error seen frequently in pre-neurosurgical head injury (HI) care that may result in serious adverse effects. This study explored this medical error amongst HI patients in a Nigerian neurosurgery unit. Methods We performed a cross-sectional analysis of a prospective cohort of HI patients who were administered mannitol by their initial non-neurosurgical health care givers before referral to our center over a 22-month period. Statistical Analysis A statistical software was used for the analysis with which an α value of <0.05 was deemed clinically significant. Results Seventy-one patients were recruited: 17 (23.9%) from private hospitals, 13 (18.3%) from primary health facilities (PHFs), 20 (28.2%) from secondary health facilities (SHFs), and 21 (29.6%) from tertiary health facilities (THFs). Thirteen patients (18.3%) had mild HI; 29 (40.8%) each had moderate and severe HI, respectively. Pupillary abnormalities were documented in five patients (7.04%) with severe HI and neurological deterioration in two with mild HI. Mannitol administration was deemed appropriate in only 43.7% (31/71). Data on mannitol dosing in 60.6% (43/71) of the patients showed 8/43 (18.6%) receiving continuous 10% mannitol infusion. The remaining 35/43 received mannitol as a 20% solution but also showing dosing error in 62.9% (22/35): overdosing in 7/35 (20%), and nonbolus administration in 15/35 (42.9%). The distribution of the dosing error among the referring health facilities (all the 13 [100%] patients from private hospitals, 66.7% from PHF, 60% from SHF, and 45.5% from THF) showed a trend of better performance ( p = 0.002) by the THFs. Conclusion Mannitol use is apparently fraught with an understudied medical error in the pre-neurosurgical care of the head injured., Competing Interests: Authors’ ContributionsConflict of Interest A.O. A.: concept, design, definition of intellectual content, literature search, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing, manuscript review, and guarantor; T. A. O.: concept, design, definition of intellectual content, literature search, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing, and manuscript review; T. A. M.: concept, definition of intellectual content, literature search, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing, and manuscript review; and O. E. O.: concept, definition of intellectual content, data acquisition, data analysis, statistical analysis, manuscript preparation, manuscript editing, and manuscript review. None declared., (Association for Helping Neurosurgical Sick People. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).)