Many a time, welded joints contain a welding imperfection having the form of an excessively wide butt weld with reference number 5212 in PN-EN ISO 6520-1. The fact that the effect of the above-named imperfection on the service life of welded joints had not been identified before inspired research aimed to fill the above-named gap. The study discusses the results of fatigue tests of welded joints having excessively wide welds and contains conclusions based on the test results. In general, the presence of welding imperfection 5212 in welded joints is highly undesirable.