The route number H98 dates back to 1 December 1990, and was the straight renumbering of a previous route 98. The original route 98 dates back much longer, more than 50 years, once runПing between Hounslow Garage and Ruislip Station, from Uxbridge and Hounslow Garages. The Hounslow allocation was withdrawn in April 1958. The route was extended from Ruislip to North Harrow, replacing the withdrawn route 221 on 1 December 1954. The Monday to Friday service was replaced by routes 98A and 98B, with the 98 only runПing on Saturday and Sunday from 23 January 1957, until 10 May 1961 when the Sunday service was withdrawn, being replaced by a Sunday service on route 98A. The Monday to Friday service was re-introduced on the withdrawal of the Monday to Friday service on route 98A. The route ran from Hounslow to Hillingdon (Monday to Friday), Ruislip (Monday to Friday peak) and North Harrow (Saturdays).
The structure was changed once again in 24, on 20 March with the Ruislip to North Harrow section being withdrawn, replaced by a Saturday service on route 98B. On 15 June 1968 the route was extended Monday to Friday peak journeys to Ruislip. A Sunday service was also introduced only between Hayes and Hillingdon, although this was withdrawn on 19 July 1969, and converted to single deck AEC Swifts on 6 January 1973. The extension to Ruislip was withdrawn on 23 January 1977.
The Sunday service was reintroduced on 22 March 1980, runПing between Hayes and Hillingdon, but this was short lived, and was withdrawn on 27 September. The Swifts were replaced by Leyland Nationals at the same time, and in turn replaced by Metrobuses during February 1984. A Hounslow Garage allocation was introduced in March 1987, and the Uxbridge allocation was withdrawn completely by May 1989.
The route was diverted at Hayes to serve Hillingdon Hill Coney Green instead, and withdrawn from Uxbridge, with the section between Hillingdon and Uxbridge being replaced by the new Uxbridge U routes, route U2. on 27 May 1989. The route was renumbered H98 on 1 December 1990.