Abstract: This paper explores issues related to the appearance and performance of fusion splices conducted with dissimilar types of single mode fiber. For long distance telecom networks, dissimilar single mode fiber splices have been used as it is sometimes desirable to mix different types of G.655 non-zero dispersion shifted fibers. The G.655 fibers will be spliced to standard G.652 fibers at patch panel locations. In recent years, dissimilar SMF splices have become increasingly common throughout telecom networks with the proliferation of bend-insensitive (G.657) fiber types as well as low-loss pure-silica core (G.654) single mode fibers. In splices of dissimilar single mode fibers, there is frequently a vertical shadow or line at the splice point which is visible in the spliced fiber image on the LCD screen of the fusion splicer. We present an explanation of the cause of the visible line and explore the optical performance as well as the strength and integrity of such dissimilar SMF splices.