Abstract Background: The mitotic spindle apparatus (MSA) is a unique structure of microtubules and associated proteins involved in the segregation and reorganisation of chromosomes during cell division. Autoantibodies to the MSA (anti‐MSA) are reported to occur rarely, but are easily identified during the immunofluorescent detection of anti‐nuclear antibodies (ANA), and are generally reported as part of that investigation. Aims: As the clinical significance of these antibodies is unknown, our aim was to identify the clinical features of subjects identified with anti‐MSA, and in a subset investigate the co‐association with organ specific anti‐thyroid antibodies. Methods: All ANA results from the three major immunology laboratories serving South Australia between January 1993 and June 1998 were retrospectively reviewed to identify anti‐MSA subjects. Clinical details were extracted from hospital or general practice records using a standard proforma. Thyroid autoantibodies were measured using standard technique. A control group of consecutive ANA positive, anti‐MSA negative individuals had anti‐thyroid antibodies measured. Statistical comparison used χ2 test. Results: Fifty‐five subjects (43F) were identified with mean age 59.8 (range 17–91); 39 had specific diagnoses, with 16 identified as part of non‐specific investigations. ‘Arthritis’ broadly accounted for the largest group, transient inflammatory arthritis n=7, degenerative joint disease n=6, rheumatoid arthritis n=5. Adenocarcinoma and mesothelioma accounted for one case each. Thirty‐two subjects had anti‐thyroid antibodies tested, with ten of 21 and two of 11 positive among the groups with anti‐MSA titre >1:80 and <1:40 respectively, χ2=2.7, p=0.1. Anti‐thyroid antibodies were detected more frequently among the high titre anti‐MSA group (ten of 21) compared with high titre positive ANA, negative anti‐MSA group (two of 11), RRisk 4.4, χ2=5.34, p=0.02. Conclusion: This study confirmed the relative rarity of anti‐MSA and that its association is primarily with rheumatic diseases. The coincidence of mesothelioma is novel with only two previous reports of malignancy and anti‐MSA. The co‐association of high titre anti‐MSA and thyroid autoantibodies suggest that the latter should be a follow up investigation if the former is identified as part of an investigative screen.