This article describes the design and development process of an eye tracking-based computer system that benefits from the intact ocular motor control of the completely locked-in patient to provide him or her with an alternative means of communication. A completely locked-in patient is an individual who has lost all types of motor control and communication ability with people in his or her environment. This developed system uses a head-mounted web camera to capture real-time images of the patient's eye. These images are then passed to a program, developed using Matlab, which processes them and computes the coordinates of the pupil position. The program then sends commands to an interactive JAVA-based interface, which provides the patient with a matrix of pictograms representing the most essential daily communication activities. When a pictogram is activated (clicked), the system plays back an audible statement, recorded in any language, reflecting the desired activity. Ten healthy adult volunteers, free from any musculoskeletal or neurological disorders, participated in the validation of the system. Validation results revealed a system accuracy of 96.11+/-5.58 % and repeatability of 94.44+/-2.51 %. The rehabilitative system developed in this project offers the locked-in patient, of any social class, the ability of simple yet effective communication. The advantages of this system over existing systems are low cost, low processing power, ease of operation, little training requirements, minimal disturbance to the patient, and ease of customization to any mother tongue.