Pedophiles constitute a heterogeneous group of sex offenders. Direct physiological assessment of sexual arousal has significantly increased our diagnostic skill and capability of monitoring treatment response. Erectile response studies have indicated that the majority of pedophiles and incest offenders show arousal to other paraphilias and frequently to appropriate adult sexual stimuli. Many sexual offenders deny or minimize their problem during initial interviews, but when confronted with laboratory results indicating deviant sexual arousal, they often acknowledge and elaborate on the paraphilia(s). Complete data and diagnoses are crucial in integrating treatment in the cognitive-behavioral paradigm.