Around 30 feet of lead flashing has been stolen from the roof of Lincoln Theatre Royal on Clasketgate.
It is believed that the theft took place at some point overnight between August 27-28, but it was only discovered on September 18 after roof checks.
Due to the sheer amount of lead stolen, it is believed that the offenders may have used a car or van to transport the stolen goods.
Police are appealing for information, and investigating officer PC Simon Berger is keen to hear from anyone who saw or heard anything suspicious in the area of the Theatre Royal on or around that date.
They can call 101 (incident 170 of the September 18) if they know something that could assist in bringing these offenders to justice, police said.