BackgroundDespite the involvement of general practitioners, the mailing of several recall letters and of the faecal occult blood test (FOBT) kit, the uptake remains insufficient in the French colorectal cancer-screening programme. Some studies have demonstrated a greater efficacy of tailored telephone counselling over usual care, untailored invitation mailing and FOBT kit mailing. We evaluated the feasibility and the effectiveness of telephone counselling on participation in the population-based FOBT colorectal cancer-screening programme implemented in Alsace (France). MethodsUnderusers were randomized into a control group with untailored invitation and FOBT kit mailing (n=19,756) and two intervention groups for either a computer-assisted telephone interview (n=9367), system for tailored promotion of colorectal cancer screening, or a telephone-based motivational interview (n=9374). ResultsOnly 5691 (19.9%) people were actually counseled, so that there was no difference in participation between the intervention groups taken together (13.9%, 95% confidence interval [CI] [13.5–14.4]) and the control group (13.9%, 95% CI [13.4–14.4]) (P=1.0) in intent-to-treat analysis. However, in per-protocol analysis, participation was significantly higher in the two intervention groups than in the control group (12.9%, 95% CI [12.6–13.2]) (P<0.01), with no difference between computer-assisted telephone interview (24.6%, 95% CI [22.7–26.4]) and motivational interview (23.6%, 95% CI [21.8–25.4]) (P=0.44). ConclusionThere was no difference of effectiveness between tailored telephone counselling and untailored invitation and FOBT kit mailing on participation of underusers in an organized population-based colorectal cancer screening programme. A greater efficacy of telephone counselling, around twice that of invitation and FOBT kit mailing, was observed only in people who could actually be counseled, without difference between computer-assisted telephone interview and motivational interview. However, technical failures hampered telephone counselling, so that there was no difference in intent-to-treat analysis. The rate of technical success of telephone interviews should be evaluated, and enhanced if insufficient, before implementation of telephone counselling in population-based cancer screening programmes.