Objective: Oocytes available for ICSI often possess defined areas of cytoplasmic granularity. Speculation over potential harmful effects of direct invasion of this granular area caused us to study this phenomenon in more detail. The objective of this study was to determine if the location of the granular area in an oocyte relative to the site of sperm injection had any impact on the rate of fertilization and subsequent embryo development in vitro.Design: A retrospective analysis of patients undergoing ICSI in a university-based ART program in which the area of cytoplasmic granularity was documented and outcomes measured.Materials and Methods: Video recordings and hand drawn representations of 2276 oocyte injections between January 1995 and December 1996 were reviewed. Oocytes were grouped according to the location of cytoplasmic granularity prior to injection: Group A: Cytoplasmic granularity was located in the 9 o'clock position where the needle directly entered the grainy area; Group B: Cytoplasmic granularity resided at the 6 or 12 o'clock position where the needle bypassed the grainy area; Group C: Cytoplasmic granularity resided at the 3 o'clock position where the needle passed directly through the grainy area and Group D: the entire cytoplasm of the egg appeared granular prior to injection. For each injection the oocyte was positioned on the holding pipet at the 9 o'clock position while injections were performed at the 3 o'clock position. The oocyte was oriented on the holding pipet by placing the polar body in the 6 or 12 o'clock position, regardless of the location of the granular area. Following injection, oocytes were returned to culture medium and fertilization was assessed 16 hrs later. Embryo evaluations were performed 28 hrs post-injection and graded according to the systems of Puissant and Steer. A one-way analysis of variance was used to determine treatment differences in the outcome variables. A power analysis was performed to determine the probability of detecting a clinically meaningful difference in fertilization (10%) and degeneration (3%) rates.Results: There was no significance between treatment groups A, B, and C in terms of fertilization, polyploidy and cleavage rates as well as embryo quality grades. A significant difference was found in the fertilization and degeneration rates of eggs that were completely granular (Group D). The fertilization rate of these oocytes was lower (P < 0.05) and the degeneration rate was higher (P < 0.005) when compared to other treatment groups. A power analysis revealed a power of 0.975 for detecting a 10% difference in fertilization rate and a power of 0.88 for detecting a 3% difference in degeneration rate.Conclusion: The area of cytoplasmic granularity in relation to the site of sperm injection does not affect subsequent fertilization and development of ICSI oocytes. In oocytes where the cytoplasm was completely granular, lower success rates were found. This may have had more to do with the quality of the oocyte rather than the location of cytoplasmic granularity.