Objective. To assess the level of compliance with follow-up over time after treatment for preinvasive and Stage Ia1 lesions of the cervix. To compare the average interval between visits with the interval prescribed by protocol and to evaluate the use of this difference as a measure of compliance. Design. Retrospective observational study. Setting. London university hospital. Population. Women who received treatment for preinvasive (CINI-III, AIS) or Stage Ia1 cervical lesions. Methods. Attendance data were obtained from hospital-based colposcopy and community-based databases. Main outcome measures. The average interval between the appointments attended by each woman was compared with the planned interval between visits. The time that elapsed since the previous appointment attended was calculated for each visit and correlated with the time since treatment. Results. 1013 women attended 4128 follow-up visits in the colposcopy clinic and in the community. Twenty-two (2.2%) women never attended any post-treatment appointment and 209 (21.0%) of the 991 women who attended at least once, did so on average more than 12 months later than specified by the follow-up protocol. There was a highly significant correlation between the interval since the previous appointment and the time since treatment (Kendall's tau b = 0.529614, two-sided p < 0.0001), showing that compliance deteriorates with increasing time since treatment. Conclusions. Comparing the average interval between attendances with the planned interval prescribed by protocol is a sensitive measure of compliance. Compliance with follow-up deteriorates significantly with time since treatment. This decline in compliance may contribute to the increased risk of invasive disease after treatment.