Background: The concept of unmet needs refers to the difference between health services necessary to treat a particular health problem and services actually received. Aim: This study examined the prevalence of self-reported unmet needs for health care and the extent to which they were attributable to perceived problems with service availability or accessibility or acceptability. Study design: descriptive analytical study. Sample: 1316 individuals Clients from some out patients, clinic of Ain Shams University hospitals. Setting: out patients, Clinic of Ain Shams University Hospitals, Cairo, Egypt. Subjects: patients randomly chosen from out patients, clinic of Ain Shams University hospitals. Tools of the study: A questionnaire tool developed to collect data about the prevalence of unmet needs for health care in the previous 6 months. Results: This study conducted on 1316 individuals where 580 (44.8%) reported unmet health care needs. As regard causes of unmet needs, 33.6% of unmet needs attributed to accessibility problems, while service availability problems accounted for 57.4% of the unmet needs. The largest group, accounting for 92.4% of unmet needs was acceptability problems. Conclusions: The causes of unmet needs attributed to accessibility and availability problems. The most common reported reason for an unmet health care need was that the too long waiting time, and the high cost of examination. Recommendations: Re-plan health care service to treat causes of unmet needs, which attributed to accessibility and availability problem. Key words: Prevalence - Unmet health care needs- availability, accessibility, acceptability reasons