Thrombotic microangiopathy is a rare haematological emergency which encompasses the conditions of haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). It is an unusual but recognised complication of chemotherapy. It has not previously been described in conjunction with docetaxel or trastuzumab therapy. We report a 47-year-old patient with localised breast cancer who developed thrombotic microangiopathy (HUS/TTP) acutely following concurrent neoadjuvant therapy with trastuzumab and docetaxel. We demonstrate from our case that mild confusion occurring on a background of mild anaemia and thrombocytopenia may sometimes be the only clue to the diagnosis. Clinicians should be aware of the possibility of thrombotic microangiopathy associated with trastuzumab and docetaxel therapy, as early intervention can improve clinical outcome.