The authors report the incidences and the effects of heterotopic ossification after 168 femoral head replacements in 162 patients who were treated at Chonnam University Hospital from January 1979 to December 1988 and were followed up at least 1 year. Heterotopic ossification developed in 52 hips (31% ) of the total 168 replaced hips. The degrees of heterotopic ossification (Brocker at al classification) were clsss I in 20 hips (38.5%), class II in 21 (40.4%), class III in 11 (21.1%) and class IV which can disturb hip function was not occured. Significant differences of the incidence of heterotopic ossification were noted between femoral neck fracture group(34 hips of 133) and trochanteric fracture group (11 hips of 16) (p<0.001), and between cemented stem group(34 hips of 84) and uncemented group(18 hips of 84) (p<0.009). There were no significant differences of the incidence of heterotopic ossification between sexes, age groups and types of prosthetic head. In conclusion, the incidence of heterotopic ossification following hemiarthroplasty was as high as in total hip replacements, however the degree was mild and it did not deteriorate the hip function.