Substantiated sibling incest, the most common type, showed a significant pattern of common dynamics to the Boulder County Sexual Abuse Team (Colorado) over 3 years and 7 months. Parents, especially fathers, were inattentive or absent through work or distance. There was no parental supervision. Either repression including rebellion or premature stimulation through observed parental sexual activity occurred. Families disintegrated through secrets, especially parental unfaithfulness. Parental incest often preceded sibling incest, and parents sexually abused 72 percent of their children. Most sibling perpetrators were male; with an average age of 11 years. The average child victim was 9 years of age. 10 references. (Author abstract modified)