The USCCB commissioned a study some time back on the statistics here. I have only come across a dead link to it thus far.
Edit: try these.
usccb.org:8765/query.html?col=&qt=pederastry&Go.x=0&Go.y=0&Go=Go
< edit: a summary >
Church records indicate that 4,392 priests were accused of engaging in sexual abuse of a minor between 1950 and 2002.11 This number represents four percent of the 109,694 priests in active ministry during that time. There were approximately 10,667 reported minor victims of clergy sexual abuse during this period, and the Church expended more than half a billion dollars in dealing with the problem.
Eighty-one percent of the victims were male. Although more than three-quarters of the victims were of an age such that the conduct does not meet the clinical definition of pedophilia, there were substantial numbers of very young children who were victimized by priests during this time period. In addition, although many of the reported acts of sexual abuse involved fondling or unspecified abuse, there was also a very large number of allegations of more grave abuse, including acts of oral sex and intercourse.
The number of priests who engaged in sexual abuse of minors and the number of victims of that abuse changed dramatically during this time period. Although there were reported acts of sexual abuse of minors in every year, the incidence of reported abuse increased by several orders of magnitude in the 1960s and 1970s. After peaking in the 1970s, the number of incidents decreased through the 1980s and 1990s even more sharply than the incidence rate had increased in the 1960s and 1970s.
The incidence of sexual molestation of a minor under eleven years of age did not vary as greatly throughout the period as did the incidence of molestation of older children. In addition, the incidence of abuse of females did not change as dramatically as did the incidence of abuse of males. There was, however, a more than six-fold increase in the number of reported acts of abuse of males aged eleven to seventeen between the 1950s and the 1970s.
Finally, the data indicate that the problem of sexual abuse of minors by priests affected all areas of the country, and not simply certain dioceses that have received sustained public scrutiny, but there was significant variation from diocese to diocese. Some dioceses, even certain large dioceses, had very few or no reported acts of sexual abuse whereas many other dioceses had twenty-five or more priests with accusations of sexual abuse of minors, and one diocese reported that 165 priests in the diocese had been accused of sexual abuse of minors.