His major work
Tzitz Eliezer is an encyclopedic treatise on halachic questions, viewed as one of the great achievements of halachic scholarship of the 20th century. Though he wrote numerous books and articles in all fields of
halacha, he was best known for his decisions on
medical dilemmas. He addresses in his volumes complex medical questions including
fertility,
abortion,
organ transplantation,
euthanasia,
sex reassignment surgery,
autopsies,
smoking,
cosmetic surgery, and medical experimentation. His halachic opinions are valued by rabbis across the religious spectrum. Waldenberg forbade performing elective surgery on someone who is neither sick nor in pain, such as cosmetic surgery. He argues that such activities are outside the boundaries of the physician's mandate to heal. Notably, Rabbi
Moshe Feinstein disagreed with this opinion. He allowed
first trimester abortion of a
fetus which would be born with a deformity that would cause it to suffer, and termination of a fetus with a lethal fetal defect such as
Tay–Sachs disease up to the end of the
second trimester of
gestation. He ruled that a child conceived outside the womb, through
in vitro fertilization, has no parents and bears no halachic relationship either to the biological parents or the "
surrogate mother", the woman who carries the child to term. He was one of a small but growing number of rabbis to forbid smoking. Many of his medical opinions were recorded by his student
Avraham Steinberg, and then translated into summary volumes. In the chapter entitled "On the treatment which exposes the physician to danger", Waldenberg wrote: Waldenberg ruled
sex reassignment surgery to be permissible in the case of a baby born androgynous where one set of organs were more developed. After careful halachic and medical consideration, Waldenberg ruled that a transsexual woman following sex reassignment surgery (SRS) is a halachic woman. He wrote, "The external anatomy which is visible is what determines the halakha" in the present tense. Nonetheless, he affirmed the universal position in Orthodox Judaism that voluntary SRS is prohibited by Halacha. ==Kevod habriyot==