An analysis was made of 19 cases of myospherulosis seen on fine needle aspirates of mammary and subcutaneous tissue masses. Myospherulosis, best seen with the Papanicolaou stain, appeared as 4 microns to 7 microns spherules that were homogeneously smooth or contained one or more internal dense bodies. The spherules were dispersed singly or aggregated into sac-like structures. Myospherulosis accompanied 16 benign and 3 malignant conditions. In two aspirates, myospherulosis was seen simultaneously with breast carcinoma; in another, fat necrosis with myospherulosis masked an underlying breast malignancy. In 10 of the 12 aspirates from patients with previous tissue trauma, it accompanied evidence of fat necrosis and mesenchymal repair; in 4 aspirates, no other underlying condition was apparent. These findings indicate that myospherulosis is not an uncommon finding in fine needle aspirates of fatty sites; it often accompanies fat necrosis and mesenchymal repair. The presence of myospherulosis in aspirates of clinically suspicious masses does not exclude an underlying malignancy.