Koscina had studied physics at the University of Naples and was "Miss Di Tappa" at the Tour of Italy bicycle race in 1954, as well as being a fashion model. She made a fleeting appearance in the part of an aspiring Actress in Siamo uomini o caporali? (Are we men or corporals?, 1955) before making a flying catch at her great opportunity: she portrayed Giulia, daughter of the train Engineer Andrea, in Pietro Germi's Il ferroviere (The Railroad Man) (1956). Koscina immediately confirmed her talent in Guendalina (1957), where she had no difficulty playing the part of a young mother.
A lead player in popular comedies, such as Nonna Sabella (Grandmother Sabella,1957), Ladro lui, ladra lei (He a thief, she a thief, 1958), and Poveri milionari (Poor millionaires, 1958), Koscina alternated cleverly between roles as vamp and ingenue. She represented women in search of social upward mobility, the image of an Italy that had left its worst problems behind.
Koscina was suited to sophisticated comedies like Mogli pericolose (Dangerous wives, 1958), where she made a direct sentimental challenge to poor Giorgia Moll. She played Hercules' fiancée in Le fatiche di Ercole (Hercules, 1958), a prototype of this kind of film. In Italy, a police officer let her go without issuing a traffic ticket. Later, as a guest on a television program, she thanked the policeman, thus getting him into trouble with the police department. The incident and its aftermath inspired the movie Il vigile (The Traffic Policeman, 1960), in which she played herself.
From the early 1960s, she invested most of her considerable earnings in a luxurious villa, in the well-to-do district of Marino, Rome, complete with 16th-century furniture and artistic paintings. That lasted until her spending overcame her dwindling income, and she had to face a tax evasion inquest, when she was forced to sell her house in 1976. Living with Raimondo Castelli since 1960, they did not marry due to then Italian law and because his wife Marinella refused him an annulment. Castelli and Koscina married in Mexico in 1967, but that marriage was not recognized in Italy.
Koscina had an extensive film career there. She also starred in the 1967 comedy caper Three Bites of the Apple with David McCallum, and Deadlier Than the Male (1967), in which Elke Sommer and she portrayed sophisticated professional killers dueling with Bulldog Drummond. She also played Danica in the Yugoslavian movie The Battle of Neretva, in 1969. She played a German Doctor, Bianca, in Hornets' Nest with Rock Hudson.
After passing 30, she partnered with actors such as Kirk Douglas in A Lovely Way to Die (1968) and Paul Newman in The Secret War of Harry Frigg (1967), but without any luck. Her career was given a boost in the second half of the 1960s when she was photographed bare-breasted in the Italian edition of Playboy magazine. Mauro Bolognini's L'assoluto naturale (1969) was released, complete with a "chaste" full nude shot.
Sylva Koscina died in Rome in 1994, aged 61, from breast cancer.
