Objectives: to compare the direct and indirect medical costs of patients with suspected Lyme borreliosis according to whether or not they had used an informal care pathway. Patients and methods: We retraced the care pathways of participating patients by a prospective questionnaire survey and a retrospective analysis of care records. Direct and indirect costs were estimated using a micro-costing method from different perspectives. We compared the costs of patients who had consulted a “Lyme Doctor” (informal care pathway) with those who had only used the formal care pathway. Non-parametric tests were used to test the significance of the differences between the two groups of patients. Results: Of 103 eligible patients, 49 (including 12 who used an informal health care pathway) agreed to be investigated. Five expenditures items supported entirely by patients were significantly higher for patients following an informal care pathway: productivity loss (3 041 ± 6 580 versus 194 ± 1 177 euros, p=0.01), alternative therapies (3 484 ± 7 308 versus 369 ± 956 euros), biological tests sent abroad (571 ± 1 415 versus 17 ± 92 euros, p<0.01), self-medication (918 ± 1 998 versus 133 ± 689, p=0.02) and transport (3 094 ± 3 456 versus 1 123 ±1 903 p=0.01). Conclusions: From the patient's standpoint, the informal care pathway involving consultation with a Lyme Doctor is far more expensive than the formal care pathway. More specificallay, the patient has to bear the costs of alternative treatments and repeated non-recommended examinations.