The details were stolen from the Bar Council, which represents barristers
The contact details and data records of all practising barristers in England and Wales have been stolen.
The data was taken during a burglary at the central London offices of the Bar Council, which is the professional body for barristers.
Details of direct debits and people who have complained about barristers, including witnesses, were also taken.
The Bar Council said it appeared the theft was a random burglary and that the data was well protected.
The information was contained on a laptop and four computer hard-drives, held at the Bar Council headquarters in London's Holborn.
The details of 3,000 people who pay the Bar Council by direct debit - including names, bank account numbers and sort codes - were taken, but the information is not said to contain any passwords, debit or credit card numbers, or pin numbers.
Also taken were the details of people who have made complaints against barristers, including witnesses, totalling some 1500 cases.
The break-in was discovered on Saturday morning.
The Bar Council said the "data is covered by a high level of protection and cannot be accessed readily".
Chief executive David Hobart added: "At present the signs are this was a random burglary, but to be sure we will have to wait for the outcome of the police investigation."