We present a case of a patient in Mozambique, who initiated treatment for rifampicin-resistant tuberculosis (RR-TB) without proof of resistance. For this patient, we estimated the probability of RR-TB using likelihood ratios of clinical arguments. The probability of RR-TB in Mozambique, positive HIV status, and treatment failure after a first treatment and after retreatment were included as confirming arguments, and a rapid molecular test showing rifampicin susceptibility as excluding argument. The therapeutic threshold to start treatment for RR-TB is unknown, but probably lower than 47% and should be calculated to guide clinical decisions.