World 1 (Dr. Mario World)

World 1 is a grassy-themed world in Dr. Mario World which serves as a tutorial for the game. Prior to playing a stage, Dr. Toad guides the player through a tutorial stage. The first area, or the first 20 stages give the player infinite hearts. Players start out with Dr. Mario, where players can obtain Dr. Peach or Dr. Bowser by stage 3. Players earn their first assistant, the Goomba, after beating Stage 5, as well as unlocking versus mode, staffing and the ability to add friends. Since version 2.0.0, skill summit is also unlocked and Dr. Toad is obtained as an extra doctor.

When areas are cleared, Toads of different colors appear, including purple, yellow, blue, green, and red. In the second area, Dorrie also appears after clearing it. The viruses featured in the regular stages are red, blue and yellow.