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.