Linezolid is used to treat patients with multidrug-resistant (MDR)/extensively drug-resistant (XDR)-tuberculosis (TB) cases, although clinical data on its safety, tolerability and efficacy are lacking. We performed a retrospective, nonrandomised, unblinded observational study evaluating the safety and tolerability of linezolid at 600 mg q.d. or b.i.d. in MDR/XDR-TB treatment in four European countries. Efficacy evaluation compared end-points of 45 linezolid-treated against 110 linezolid-nontreated cases. Out of 195 MDR/XDR-TB patients, 85 were treated with linezolid for a mean of 221 days. Of these, 35 (41.2%) out of 85 experienced major side-effects attributed to linezolid (anaemia, thrombocytopenia and/or polyneuropathy), requiring discontinuation in 27 (77%) cases. Most side-effects occurred after 60 days of treatment. Twice-daily administration produced more major side-effects than once-daily dosing (p = 0.0004), with no difference in efficacy found. Outcomes were similar in patients treated with/without linezolid (p = 0.8), although linezolid-treated cases had more first-line (p = 0.002) and second-line (p = 0.02) drug resistance and a higher number of previous treatment regimens (4.5 versus 2.3; p = 0.07). Linezolid 600 mg q.d. added to an individualised multidrug regimen may improve the chance of bacteriological conversion, providing a better chance of treatment success in only the most complicated MDR/XDR-TB cases. Its safety profile does not warrant use in cases for which there are other, safer, alternatives.