Purpose Thrombolysis-related haemorrhagic transformation (HT) subtypes may have different prognostic implications. We aimed to analyse the impact of cerebral microbleeds (CMBs) burden on HT subtypes and outcome after intravenous thrombolysis.

Methods We retrospectively examined clinical and radiological data from 333 consecutive patients with acute ischaemic stroke who underwent susceptibility-weighted imaging before intravenous thrombolysis. Logistic regression analysis was used to determine the impact of CMBs on HT subtypes and neurological outcome.

Results We observed 596 CMBs in 119 (39.7%) patients on initial gradient-recalled echo scans. HT occurred in 88 (29.3%) patients, among which 62 were haemorrhagic infarction and 26 were parenchymal haemorrhage (PH). Logistic regression analysis indicated that the presence of extensive (≥3) CMBs was independently associated with PH (OR 6.704; 95% CI 2.054 to 21.883; p=0.002) and poor clinical outcome (OR 2.281; 95% CI 1.022 to 5.093; p=0.044).

Conclusions The presence of extensive (≥3) CMBs increased the risk of PH 24 h after intravenous thrombolysis, and predicted poor clinical outcome independently.