This study investigated provider-based complementary/alternative medicine use and its association with receipt of recommended vaccinations by children aged 1-2 years and with acquisition of vaccine-preventable disease by children aged 1-17 years. Results were based on logistic regression analysis of insurance claims for pediatric enrollees covered by two insurance companies in Washington State during 2000-2003. Primary exposures were use of chiropractic, naturopathy, acupuncture, or massage practitioner services by pediatric enrollees or members of their immediate families. Outcomes included receipt by children aged 1-2 years of four vaccine combinations (or their component vaccines) covering seven diseases, and acquisition of vaccine-preventable diseases by enrollees aged 1-17 years. Children were significantly less likely to receive each of the four recommended vaccinations if they saw a naturopathic physician. Children who saw chiropractors were significantly less likely to receive each of three of the recommended vaccinations. Children aged 1-17 years were significantly more likely to be diagnosed with a vaccine-preventable disease if they received naturopathic care. Use of provider-based complementary/alternative medicine by other family members was not independently associated with early childhood vaccination status or disease acquisition. Pediatric use of complementary/alternative medicine in Washington State was significantly associated with reduced adherence to recommended pediatric vaccination schedules and with acquisition of vaccine-preventable disease. Interventions enlisting the participation of complementary/alternative medicine providers in immunization awareness and promotional activities could improve adherence rates and assist in efforts to improve public health.