This work contains a cytogenetic analysis of 507 consecutive CML patients examined at diagnosis before any therapeutic treatment. Philadelphia chromosome translocations different from the standard t(9;22)(q34;q11) were observed in 28 patients (5.5%). Structural chromosomal abnormalities apparently unrelated to the Ph were found in six patients carrying variant Ph (6 of 28 = 21.4%) and in three patients carrying standard Ph translocations (3 of 472 = 0.6%). This finding confirms that structural abnormalities other than Ph are a rare event at diagnosis but that they occur with significantly different frequencies between the variant and standard Ph translocations, indicating that causes favoring the variant Ph formation may promote additional non-lethal DNA breakpoints.