Inspect the shower ceiling for mold. Wash the mold away with soap and water using a sponge and dry with a cloth. If the mold problem is too large, go to Step 2.
Pull down the damaged portion of the shower ceiling. Put on safety goggles and a dust mask. Score an outline around the damaged area 4 to 6 inches larger than the affected ceiling. Use a reciprocating saw if necessary. Square the damaged portion so it is even on all sides.
Measure the cut-out section with a tape measure and write down the dimensions. Mark and cut a section of drywall from a new moisture-resistant drywall panel to patch the shower ceiling.
Fasten the new drywall to the ceiling beams with drywall screws using a screw gun. If no beams are immediately above the cut-out section, cut 2-by-4-inch lumber to fit with a circular saw. Fasten the lumber to the nearest ceiling beams with a nail gun. Tape the joints with drywall tape and spread joint compound over the whole patch with a putty knife, including the taped joints.
Sand the patch thoroughly to prepare it for primer and paint to conceal the patch. Make the joints smooth and even to better conceal the patch.
Apply a coat of primer to the patch with a roller, extending a few inches beyond the patch's borders. Let the primer dry for at least two to three hours. Apply the first coat of paint with a roller. Allow the first coat to dry to determine how many more coats will be needed to match the rest of the shower ceiling. Apply additional paint coats as necessary.