4 Volumes. Very good. Easy to read, with the focus being on differentiating similar conditions. Bought this series on recommendations of several friends. It is worth the investment. Probably a bit more popular in the USA than here. Online access. Whilst not nearly as comprehensive as Dahnert/ Allison & Grainger, this provides an excellent overview.
Couple of criticisms:
1 - whilst the list of chapter headings is on the inside cover of each volume, the complete index for all four volumes is at the end of volume 4. This is a bit weird but tolerable.
2 - Some topics are organised by modality rather than specialty. This means finding bits of information in several places rather than in one (and only one) place.
On balance, these are minor faults and I'm glad to have bought these books. Particularly well written sections are MSK (Helm's text), GI and Neuro.