Frank Castillo, a right-handed pitcher, embarked on his Major League Baseball career when he was drafted by the Chicago Cubs in the sixth round of the 1987 MLB Draft. He made his debut with the Cubs on June 27, 1991, marking the beginning of a career that spanned over a decade in the major leagues. Castillo quickly became a regular in the Cubs' starting rotation, showcasing his skills on the mound with a mix of fastballs and breaking pitches.

During his tenure with the Cubs, Castillo experienced both highs and lows. One of his most memorable performances came on September 25, 1995, when he came within one out of pitching a no-hitter against the St. Louis Cardinals. Despite losing the no-hit bid, this game highlighted his potential and ability to dominate opposing hitters. Castillo's time with the Cubs lasted until 1997, after which he was traded to the Colorado Rockies.

His stint with the Rockies was brief, as he was traded to the Detroit Tigers in 1998. Castillo's journey through the majors continued as he moved from team to team, including the Toronto Blue Jays and the Boston Red Sox. While with the Red Sox in 2001, Castillo found a degree of stability, contributing as both a starter and reliever. His adaptability allowed him to fill various roles as needed by the team.

In 2004, Castillo signed with the Florida Marlins, where he played a part in their pitching staff. His final major league appearance came with the Marlins in 2005. Over the course of his career, Castillo compiled a win-loss record of 82-104, with an earned run average (ERA) of 4.56 and 1,101 strikeouts. These statistics reflect the challenges and achievements he encountered throughout his time in the majors.

Frank Castillo's career was characterized by perseverance and adaptability, as he navigated the ups and downs of professional baseball.