We report the results of a single-dish survey of molecular outflows towards a homogeneous sample of 136 ultracompact HII regions for which we had previously obtained observations in the methanol 6.7GHz and water 22.2GHz maser lines. The line profiles of the ^13^CO J=1-0 and 2-1 transitions have been compared to those of the corresponding lines of the C^18^O isotopomer to reveal the occurrence of line wings and hence of molecular outflows. description: The observations were carried out with the IRAM 30-m telescope at Pico Veleta (Granada, Spain) during several runs in April and August 2000.