Nowadays organisations are seeking for effective ways to compete with their competitors, where internal services play one of the main roles. The information technology (IT) service is an integral part involved in internal services, the ones usually associated with high costs. Therefore, performance appraisal of the personnel of IT department is one of the most important tasks of organisation managers. In this paper, various common appraisal models used to evaluate service quality are first introduced. Then, the SERVQUAL model is selected and customised for quality evaluation of IT departments. A case study is next presented for the application of the SERVQUAL model in the performance appraisal of the IT department of a detergent producer company. In addition, a gap analysis is used to investigate the weaknesses and strengths of the IT unit. To this aim, a radar chart is applied to the data obtained from questionnaires. Analysing the results shows that the courtesy is the main influential factor in view of the customers followed by reliability, empathy, tangibility, assurance, and responsiveness, respectively. Finally, some corrective actions are proposed to improve the performance of the IT staff.