The aim of this study was to assess the up- and download performance of an image Web system (IWS) during simultaneous up- and download procedures. Following preparatory tests, the upload capacity (UC) with and without simultaneous download and the time-to-display (TTD) with and without simultaneous upload were determined for different image, server and compression types, and with up to 16 concurrent clients. The UC varied between 1.7–5.5 Gigabyte per hour (GB/h) and was slightly influenced by a simultaneous download; however, the TTDs were substantially prolonged during an upload and only below 5 s with up to four to six concurrent clients. The choice of image and server type had a strong impact on UC and TTD. Lossy primary compression proved slightly superior. An effective UC of approximately 4.0 GB/h or 96 Gigabyte per day (GB/day) can be achieved, which appears suitable even for large institutions. Because of its substantial influence on UC and TTD during simultaneous up- and download, the server hardware should be equipped with two processors and 1 GB RAM. Lossy primary compression may be used with slight performance benefits when full-resolution images are not required. The upload is a time-demanding process, and it is possible that during peak hours the waiting times are unacceptable for clinicians.