Objective: To assess whether the number of disclosures of child abuse changed as a result of a prevention strategy on a national scale in a West- European country. The child abuse involved child sexual and physical abuse, both ongoing and past. Methods: In order to assess possible intervention effects, changes in calling the Child Line were measured. For this, a 4 year longitudinal design, starting before the intervention and ending 2 and 1/2 years after it was used (N = 3,117 disclosures). In addition, data were collected from the Dutch Telecom and a newely developed Child Abuse Form (N = 1,227). Finally, two measures were introduced, the disclosure coefficient and the relative disclosure coefficient. Results: Most calls were silent calls, a phenomenon that deserves more attention in disclosure research. Compared to pre-intervention data, the amount of disclosures almost tripled during the intervention and was even further enhanced in the post-intervention and follow-up. In nine out of 10 cases, ongoing abuse was disclosed. Marked differences between child physical abuse and child sexual abuse were observed. Conclusion: It is concluded that mass media communication, if well implemented, can positively influence the process of disclosure of ongoing child abuse.