When a Ne:BF3 sample is passed through a long stainless steel deposition line before being frozen onto a cryogenic observation surface maintained at approximately 5 K, the infrared spectrum of the resulting deposit includes prominent absorptions assigned to BF2OH and weaker absorptions contributed by F-3 B-11-OH2. Pretreatment of the deposition line with isotopically substituted water leads to the appearance of absorptions of the O-18- and D-substituted products. The assignments are supported by the results of ab initio calculations at several different levels and by a least-squares force constant fit to the infrared absorptions of the isotopomers of BF2OH. The thermochemistry of the reactions of BF3 and H2O to form F3B-OH2 and to form BF2OH+HF has been calculated at the G2 level. Although the heats of reaction calculated for 298 K somewhat favor formation of the complex, when the entropy is also considered the two reactions become more competitive.