PURPOSE: To determine the appropriate size of a short and long-term storage device, bearing in mind the design factors involved and the installation costs. MATERIALS AND METHODS: The number of radiologic studies quoted is the number of these undertaken during a one-year period at a university hospital with 650 beds, and reflects the actual number of each type of examination performed at a full PACS hospital . The average daily number of outpatients was 1,586, while that of inpatients was 639.5. The numbers of radiologic studies performed were as follows: 378 among 189 outpatients, and 165 among 41 inpatients. The average daily number of examinations was 543, comprising 460 CR, 30 ultrasonograms, 25 CT, 8 MRI, and 20 others. RESULTS: The total amount of digital images was 17.4 GB Per day, while the amount of short-term data with lossless compression was 6.7 GB Per day. During 14 days short-term storage, the amount of image data was 93.7 GB in disk array. The amount of data stored mid term (1 year), with lossy compression, was 369.1 GB. The amount of data stored in the form of long-term cache and educational images was 38.7 GB and 30 GB, respectively. The total size of disk array was 531.5 GB. A device suitable for the long-term storage of images, for at least five years, requires a capacity of 1845.5 GB. CONCLUSION: At a full PACS hospital with 600 beds, the minimum disk space required for the short-and mid-term storage of image data in disk array is 540 GB. The capacity required for long term storage(at least five years) is 1900 GB.