The discharge capacity of most dam spillways has been determined through physical hydraulic model tests prior to construction. In Sweden, the majority of dams were built between 1945 and 1975. When the design-flood guidelines were updated, hydrological investigations have shown that many existing dams have a spillway capacity lower than the revised design flood. This leads to the need of structural rehabilitation for a higher level of dam safety. This has necessitated many dams and spillways being re-tested in the laboratory to examine their discharge capacity and the efficiency of energy dissipation at the new higher design flood. For the same spillway layout, differences exist in the spillway discharge capacity between the previous and present model tests. A total of 17 dam spillways are included, including both surface and bottom spillway types. The new experimental test data has shown that the spillway capacity can be greater than, less than or approximately equal to the capacity determined in previous experiments. For some dams, the deviation can be as large as 8-12%. The test data has been analyzed and the possible reasons for the noted discrepancy have been explored. The primary reasons for the discrepancies are thought to be due to the model construction quality and flow measurement method. In some cases, it is found that the dam was not constructed as originally tested and there are certain, albeit minor, differences in the spillway layout, which affects the discharge.