From a new mosaic image in the H-α line of the complete disc of the spiral galaxy M100, a catalogue is composed listing 1948 individual HII regions. For each HII region, the catalogue gives its position relative to the centre of the galaxy, its deprojected distance to the centre, its radius, and its calibrated luminosity. An indication is included as to whether the HII region is located in the arms, between them, or in the circumnuclear star-forming region. The H-α image of M100 was obtained during two observing runs with the 4.2m WHT on La Palma, using the TAURUS camera in imaging mode. Since the field of view in this setup is limited by the filter size to around 5' diameter, four fields of the galaxy were imaged, two (eastern half of M100) during the night of 27 May 1991, and two (western half) during the night of 14 March 1992. Narrow band redshifted H-α filters with width of 15Å were used for the observations, centred at 6601Å for the H-α line observations (redshifted using the galaxy's systemic velocity of 1571km/s) and at 6577Å and 6565Å for the continuum. Exposure times were 1200 seconds for both the on-line and the continuum image on the first night, and 2x900 seconds on the second night. An EEV CCD chip was used during both observing runs, with a projected pixel size of 0.279arcsec, and a size of 1180x1280 pixels. (1 data file).