The 1990–91 Australian region cyclone season was a slightly below average cyclone season, with ten tropical cyclones occurring within the region between 90°E and 160°E. The season officially ran from November 1, 1990, to April 30, 1991, with the first disturbance of the season forming on 10 December and the last disturbance moving out of the region during 11 May. Six people were killed by Cyclone Joy when it made landfall on Australia. During the season, tropical cyclones were monitored by the Australian Bureau of Meteorology, who ran Tropical Cyclone Warning Centers (TCWC) in Perth, Darwin, and Brisbane. The United States Joint Typhoon Warning Center (JTWC) and Papua New Guinea National Weather Service also monitored systems within the basin during the season. The JTWC designated systems with a number and either a S or a P suffix depending on which side of 135E. The Bureau of Meteorology and Papua New Guinea national Weather Service both used the Australian Tropical Cyclone Intensity Scale, and estimated windspeeds over a ten-minute period, while the JTWC estimated sustained winds over a one-minute period and are comparable to the Saffir–Simpson Hurricane Scale.

The 1990–91 South-West Indian Ocean cyclone season was fairly quiet, although activity began early and the final named storm formed at a record late date. There were seven named storms classified by the Météo-France office (MFR) on Réunion, as well as three depressions; an additional depression was classified by the Joint Typhoon Warning Center (JTWC), an unofficial warning agency. The JTWC tracked storms in both September and October, although neither affected land. In late November, another short-lived depression formed in the northeastern portion of the basin. Activity remained minimal until January, when Tropical Storm Alison formed in the eastern portion of the basin. Later in the month, Cyclone Bella became the strongest storm of the season, reaching 10‑minute maximum sustained winds of 155 km/h (96 mph). It passed near the island of Rodrigues, becoming the worst cyclone there in 20 years and killing half of the population of one endangered species. Bella also likely caused a cargo ship to go missing with 36 people on board. Three storms developed in short succession in the second half of February. Cyclone Cynthia developed rapidly in the Mozambique Channel on February 16 and struck western Madagascar, killing 36 people and ruining local rice harvests. A residual trough after Cynthia dissipated spawned Tropical Storm Debra, which looped in the Mozambique Channel. Toward the end of the month, Tropical Storm Elma exited the basin into the adjacent Australian region, only to re-enter the south-west Indian Ocean and dissipate. Long-lived Cyclone Fatima originated in the Australian basin in late March and changed directions before becoming extratropical. On April 2, a tropical depression struck eastern Madagascar, killing 18 people. The final storm, Gritelle, was named on June 10, the latest on record.