While the general feeling of most people, especially now that the cold war is (mostly) over, is that the risk of human extinction is extremely small, experts have assigned a significantly higher probability to the event.
In 2008 an informal poll at the Global Catastrophic Risk Conference at the University of Oxford yielded a median probability of human extinction by 2100 of 19%. Yet, one might want to be cautious when using this result as a good estimate of the true probability of human extinction, as there may be a powerful selection effect at play. Only those who assign a high probability to human extinction are likely to attend the Global Catastrophic Risk Conference in the first place, meaning that the survey was effectively sampling opinions from one extreme tail of the opinion distribution on the subject. Indeed, the conference report itself stated that the findings should be taken 'with a grain of salt'.