The main purpose of this study is to investigate the relationship between students' attitude toward learning mathematics and mathematics achievement with respect to gender in 10th-grade students in Amman, Jordan. Three instruments were used in the study to collect data; a mathematics achievement test (MAT), consisting of questions selected by the researcher from the (2004) Ohio Graduation Practice Test; an attitude questionnaire (ATM), developed by Taylor (1997) from the Aiken Scale (1976); and student interviews developed by the researcher. The overall results of the study indicate that there were significant differences in attitude and achievement between male and female students in the 10th grade (F = 16.3, p < 0.01). It also shows, using a Pearson Correlation, that there is a significant correlation between the two dependent variables; attitude toward learning mathematics and mathematics achievement. The main recommendations used in the study are for teachers and other educational professionals to focus on the attitudes of students toward mathematics in order to improve the learning of mathematics. School-wide programs should strive to build positive attitudes toward mathematics in all students. These programs should begin at the primary level and continue throughout the school career, producing positive results in the long run.