Muonium hyperfine structure and hadronic effects

A new result for the hadronic vacuum polarization correction to the muonium hyperfine splitting (HFS) is presented: Delta nu(had - vp) = (0.233 ± 0.003) kHz. Compared with previous calculations, the accuracy is improved by using the latest data on e+e- -> hadrons. The status of the QED prediction for HFS is discussed.