This paper documents the yield gains attributable to the breeding and distribution of new cocoa varieties in Ghana, using data from a 2002 survey of 192 fields in the country's key cocoa producing regions. We find that planting the more recently-released varieties is associated with at least 42% higher yields, and that genetic improvement accounts for much but not all of the observed correlation between tree age and cocoa yield. Fertilizer use is also very important, being associated with 19% higher cocoa yield per 50 kg bag of fertilizer. We find no evidence that varieties differ in their response to fertilizer, pesticide use or labour, and no evidence of a decline in the yield advantage of new varieties over the 17-year age span observed in the sample.