In a field trial in the Netherlands 765 dairy cows were treated during 869 lactations with 500 μg gonadotrophinreleasing hormone (gonadorelin4i.m.) for cystic ovarian disease (COD) between June 1987 and April 1996. COD was defined as the presence of a large follicle (> 2.5 cm) on one or both of the ovaries in the absence of a corpus luteum. Two treatment groups were formed, based on the interval from parturition to first treatment, with day 60 being the cut‐off between groups 1 and 2. The aim of this study is to examine whether there is a relationship between the moment of diagnosis and treatment (before or after day 60post partum) and its result. In group 1 90.0% of first treatments were effective and in group 2 93.3% (p=0.08). This was reflected by the slightly higher number of treatments needed for animals in group 1 (1.11 versus 1.07, p=0.08). The efficacy rate after one treatment did not significantly differ between the groups (1.63 versus 1.69, p=0.40) and nor did the interval between 1stinsemination after treatment and conception (p<0.63). In conclusion, it can be stated that gonadorelin is effective as therapy irrespective of the timing of diagnosis and treatment.