This study analyzed the relationship between type of discoid lateral menisci and tear pattern. There were 108 consecutive cases (103 patients) with discoid lateral meniscus tear treated by arthroscopy. Regarding type of discoid meniscus (Watanabe's classification), 38 cases were "complete" and 70 cases "incomplete." There was no Wrisberg type. Tear patterns were classified into simple horizontal, complicated horizontal, longitudinal, radial, degenerative, and complex tear. The relationship between tear pattern and type of discoid menisci was statistically highly significant. Simple horizontal tear was found only in the complete type of case, and radial, degenerative, and complex tears were found only in the incomplete type of case. In the longitudinal tear, however, we found no correlation between tear pattern and type of discoid meniscus. In addition, the extent of meniscal resection was dependent on the tear pattern. Subtotal or total meniscectomy was performed significantly more frequently in longitudinal and complex tears. In radial and degenerative tears only partial meniscectomy was carried out. Complicated horizontal tears showed no difference in extent of resection. Among the 13 cases of simple horizontal tears partial meniscectomy was performed in 12 cases. These findings about relationship between the type of discoid menisci and tear pattern could be useful in planning operation and deciding extent of resection.