Aim: To study nurses' compliance to national guidelines (Sweden) for peripheral venous catheters and to establish the complication frequency connected to time in situ and bore size., Background: Worldwide, there are no standard peripheral venous catheters guidelines, and the need for elective replacement has been challenged. Furthermore, the time interval and need for elective change of peripheral venous catheters has cost implications for hospitals., Design: Prospective register study., Methods: The health care professionals in one surgical ward in a university hospital in the south of Sweden prospectively registered peripheral venous catheters parameters. Four hundred and thirteen peripheral venous catheters were registered for time in situ, size and complications. A cost analysis was performed. Non-parametric statistics were used, and p<0.05 was regarded as significant., Result: Compliance to the guideline of time in situ was 30.2%, and the frequency of thrombophlebitis was 6.5%. Peripheral venous catheters left in situ for more than 72 hours caused more thrombophlebitis (p=0.03). There was no difference in thrombophlebitis rate when peripheral venous catheters were changed within 24 hours compared with peripheral venous catheters that were changed within 72 hours. No difference was seen regarding complications between peripheral venous catheters sized 0.9 mm/22 gauge or 1.1 mm/20 gauge., Conclusion: The present Swedish national guidelines, advocating peripheral venous catheter change every 24 hours, should be altered since peripheral venous catheters left in situ for up to 72 hours were not found to be related to a greater risk of developing thrombophlebitis. Nor is it compatible with a greater risk to use a peripheral venous catheter of 1.1 mm/20 gauge instead of 0.9 mm/22 gauge. The change in guidelines would decrease money spent, 250 100 Euro in Sweden, thus allowing time for the nurses to do other tasks and save discomfort for the patients., Relevance to Clinical Practice: National guidelines should be based on evidence and current facts, and evaluation of guidelines should be given priority., (© 2010 Blackwell Publishing Ltd.)