A woman's trial for murdering a three-year-old boy in her care was abandoned today after four weeks because a key medical witness was too ill to give evidence.

Patricia Angela Pickering, 38, pleaded not guilty in the High Court at Auckland for the murder of Dylan Hohepa Tonga Rimini.

She also denied two charges of causing him grievous bodily harm, and one of assault.

Dylan died in Auckland's Starship Hospital in April 2008 from head injuries.

The trial was abandoned today at the request of the Crown because of the unavailability of the medical witness due to illness.

The trial was set to run another two weeks. No date has been set for a retrial.