Naturally occurring platinum (78Pt) consists of five stable isotopes (192Pt, 194Pt, 195Pt, 196Pt, 198Pt) and one very long-lived (half-life 4.83×1011 years) radioisotope (190Pt).
There are also 34 known synthetic radioisotopes, the longest-lived of which is 193Pt with a half-life of 50 years.
All other isotopes have half-lives under a year, most under a day.
All isotopes of platinum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
Platinum-195 is the most abundant isotope.