To determine whether radiotherapy (
RT
) can increase pelvic fracture risk in rectal cancer survivors. Rectal cancer patients who underwent curative surgery between 1996 and 2011 in Taiwan were retrospectively studied using the National Health Insurance Research Database (
NHIRD
) of Taiwan.
ICD
‐9 Codes 808, 805.4‐805.7, 806.4‐806.7, and 820 (including pelvic, sacrum, lumbar, and femoral neck fracture) were defined as pelvic fracture. Propensity scores for
RT
, age, and sex were used to perform one‐to‐one matches between the
RT
and non‐
RT
group. Risks of pelvic and arm fractures were compared by multivariable Cox regression. Of the 32 689 patients, 7807 (23.9%) received
RT
, and 1616 suffered from a pelvic fracture (incidence rate: 1.17/100 person‐years). The median time to pelvic fracture was 2.47 years. After matching, 6952 patients each in the
RT
and non‐
RT
groups were analyzed.
RT
was associated with an increased risk of pelvic fractures in the multivariable Cox model (hazard ratio (
HR
): 1.246, 95% confidence interval (
CI
): 1.037‐1.495,
P
= 0.019) but not with arm fractures (
HR
: 1.013, 95%
CI
: 0.814‐1.259,
P
= 0.911). Subgroup analyses revealed that
RT
was associated with a higher pelvic fracture rate in women (
HR
: 1.431, 95%
CI
: 1.117‐1.834) but not in men, and the interaction between sex and
RT
was significant (
P
= 0.03). The
HR
of pelvic fracture increased 2‐4 years after
RT
(
HR
: 1.707, 95%
CI
: 1.150‐2.534,
P
= 0.008). An increased risk of pelvic fracture is noted in rectal cancer survivors, especially women, who receive
RT
.