An areawide program for biological control of the alfalfa weevil showed expected economic benefits of $2.2 billion, expressed in present value terms. Alfalfa producers and consumers of livestock products are the main beneficiaries. The control program was highly successful, with a benefit/cost ratio of about 91. Not all areawide biological pest control programs will be as successful; a benefit-cost analysis like the one described here should be performed before areawide control is initiated to identify programs expected to provide economic benefits.