An inspection into Glasgow Royal Infirmary found nursing staff on several wards had to repeatedly challenge medical staff to obey strict rules over dress code and infection control.
Three separate doctors were seen wearing a wrist watch, having long hair untied and wearing an outdoor jacket at bedsides.
Inspectors issued the hospital with requirements to improve its performance in preventing hospital acquired infections.
The report said in general there was good compliance with the dress code policy but said some medical staff did not comply.
The inspection team from Healthcare Improvement Scotland gave the hospital one month to ensure staff stick to the code.
It issued four requirements, including ensuring all patient equipment was stored and cleaned in one ward to reduce contamination risk, after three commodes and other equipment were found to be contaminated.
The report said inspectors checked another 17 commodes and found them and the majority of patient equipment to be clean.
The chief inspector said the board was making good progress to protect patients, staff and visitors from acquiring an infection.
Health bosses said a plan has been devised to address dress code compliance.
Rory Farrelly, NHS Greater Glasgow & Clyde Acute Director of Nursing, said: "We were pleased to note the number of positive findings by the HEI inspectors since their last visit.
"In particular, we were pleased the inspectors noted the good communication between nursing and domestic staff in all wards, and the effective communication and support between the infection control team and ward staff.
"There was also clear evidence of good hand hygiene practice and overall the areas inspected were found to be clean. However, we recognise there are still areas we need to address."