Background: Alopecia areata (AA) is an autoimmune disorder of the hair follicle characterized by inflammatory cell infiltrates around anagen hair follicles. The ultrasound biomicroscopy (UBM) technique generates high resolution echographic images using acoustic frequencies between 20 and 200 MHz which enables non-invasive visualization of cutaneous structures. Objective: To detect the accuracy of ultrasound biomicroscopy (UBM) in evaluating cases of alopecia areata and detecting the changes in hair follicles through correlating its findings with clinical and pathological assessment. Methods: Thirty patients with AA above the age of 18 years underwent history taking & full clinical examination. UBM examination of an area of AA in the scalp was done in all patients followed by punch biopsy (4 mm) for histopathological examination. In cases of patchy alopecia the same was done in a normal area of scalp as a control. Results: No significant difference was found between UBM imaging and histopathological assessment as regards number of hair follicles in areas affected by AA (P:0.655) as well as in control areas (P:0.102) with a significant positive correlation (P:<0.001, r:0.870) denoting that the UBM findings reflect sensitively the histopathological changes in the scalp in the area imaged. This was also the case on analyzing data of cases with patchy AA and those with AT and AU separately. A negative correlation was found between the number of follicles in UBM imaging of areas of AA and duration of illness (P: 0.05, r:-0.358) meaning that the longer the disease duration the fewer the number of hair follicles. Similarly there was no significant difference between UBM imaging and histopathological assessment as regards the width of the hair follicles (P: 0.102). A negative correlation was also found between the width of the follicles in UBM imaging of AA areas and the duration of illness (P:0,021, r:-0.428) which could be explained by the fact that two events that occur in long-standing cases which are slightly reduced inflammatory infiltration and miniaturization of hair follicles. Conclusion: In alopecia areata good or even excellent correlation between ultrasonic and histological measurements of hair follicle number and width was evident in this study; UBM examination could have clinical applications on prognosis and follow-up of cases of AA during therapy.