Background: Aceh, Indonesia, was the hardest-hit area in the 26 December 2004 Indian Ocean earthquake and tsunami, with more than 500,000 people displaced, 120,000 people dead, and total damages and losses estimated at $4.5 billion. The relief effort following the tsunami was also immense. Objectives: This study aimed to determine and assess utilization patterns of formal public versus private and mobile health services for children under age 5 with diarrhea, cough and difficulty breathing, fever, or skin disease and to identify determinants of care usage. Methods: A household survey of 962 households was administered to caretakers of children aged 1–5 years. A sample of clusters within Banda Aceh and Aceh Besar were selected and those caretakers within the cluster who fit the inclusion criteria were interviewed. Results: Of those caretakers who utilized formal health services as the first line of care for their sick child, 62% used a public health facility, 30% used a private health facility, and 8% used a mobile clinic. In terms of significant factors associated with public, private, and mobile care utilization, mobile clinics were at one side of the spectrum and private clinics were at the other side overall, with public care somewhere in between. This was true for several variables. Mobile clinic users reported the lowest cost of services and medicine and the highest perceived level of accessibility, and private care users reported the highest perceived level of satisfaction. Conclusions: Utilization of formal health services for children was quite high after the tsunami. The caretaker's perceived satisfaction with public health services could have been improved. Mobile clinics were an accessible source of health care and could be used in future disaster relief efforts to target those populations that seek less care for their sick children, including displaced populations, and those children whose parents have died.