BACKGROUND The aim of this study was to analyze the complications derived from the use of intravenous cannulae with particular attention being paid to the possible predisposing factors. METHODS A prospective follow up of 569 intravenous cannulae placed in the emergency department or the medical ward of a county hospital was carried out. 492 of these cannulae were peripheral (PC) and 77 central inserted through peripheral veins (CPVC). RESULTS Fifty-one percent of the catheters were withdrawn due to complications with the most frequent being phlebitis (35%), followed by extravasation (11.5%). The mean time in situ was 3.61 +/- 3.2 days. The daily risk of complications ranged from 2 to 9% for the CPVC (non significant differences) and between 15% (day 1) and 30% (6 or more days) for the PC. In the latter case there were no differences in the daily specific rate of complications after the first 24 hours. The probability of a catheter remaining in place more than three and six days without complications was 51% and 31%, respectively for the CP and 91% and 87% for the CPVC (p < 0.0001). Of the variables analyzed, age > 65 years, female sex, insertion of the cannula into the back of the hand, the fact of the route being peripheral without the administration of heparin were significantly associated to the development of complications, while the intravenous administration of aminophillin was associated with the appearance of phlebitis. Thirteen percent of the catheters withdrawn due to phlebitis were infected. CONCLUSIONS The complication most frequent observed in intravenous cannulation was phlebitis, an entity which is generally not of an infectious nature. The risk of unspecific complications every day during catheterization is constant in the case of central peripheral vein cannulae as well as in peripheral cannulae which do show problems during the first 24 hours after placement. Insertion of the cannulae into the veins of the back of the hand, female sex, advanced age and intravenous administration of certain drugs influence in the development of phlebitis.