Tropical cyclones rank above earthquakes as the major geophysical cause of loss of life and property (Bryant, 1991; Houghton, 1994). In the United States alone, the damage bill from mainland landfalling hurricanes over the last 50 years averages $2.0 billion per year (Hebert et al., 1996). Years with high numbers of hurricanes provide new insight on the environmental factors influencing interannual variability; hence the interest in the exceptional 1995 Atlantic season which saw 11 hurricanes and a total of 19 tropical storms, double the 50-year average. While most environmental factors in 1995 were favourable for tropical cyclone development, we show that a factor not fully explored before, the sea surface temperature (SST) was the most significant. For the 10¿--20 ¿N, 20¿--60 ¿W region where 93% of the anomalous 1995 hurricanes developed, ~45 year statistical regressions show that SST is the dominating influence, independent of all known other factors, behind the interannual variance in Atlantic hurricane numbers. With this SST experiencing record warm levels in 1995, 0.66 ¿C above the 1946--1995 mean, these regressions indicate that sea warming explains 61¿34% of the anomalous hurricane activity in 1995 to 95% confidence.¿ 1997 American Geophysical Union