A tissue containment bag, comprising: a first opening and a second opening interconnected by a sidewall of flexible material; the sidewall defining a first interior compartment configured for receiving a tissue specimen through the first opening into the first interior compartment; the sidewall forming an elongated hollow, sleeve-like neck extension defining a second interior compartment having a proximal end interconnected with the first interior compartment and a distal end interconnected with the second opening; the second opening being in fluidic communication with the second interior compartment; the second interior compartment being in fluidic communication with the first interior compartment and the first interior compartment being in fluidic communication with the first opening; the proximal end of the neck extension being connected to the sidewall of the first interior compartment at a first side; the neck extension extendable laterally in a direction away from the first side; the sidewall at the first interior compartment having a width perpendicular to a first longitudinal axis defined by a radial plane of the first opening when the bag is in undeflected configuration and a length along the first longitudinal axis; the neck extension having a width perpendicular to a second longitudinal axis defined by a radial plane of the second opening when in undeflected configuration and a length along the second longitudinal axis; the width of the neck extension being smaller than the width of the first interior compartment; and characterized by an external pocket on the sidewall sized and configured to contain the neck extension in a folded configuration. a first opening and a second opening interconnected by a sidewall of flexible material; the sidewall defining a first interior compartment configured for receiving a tissue specimen through the first opening into the first interior compartment; the sidewall forming an elongated hollow, sleeve-like neck extension defining a second interior compartment having a proximal end interconnected with the first interior compartment and a distal end interconnected with the second opening; the second opening being in fluidic communication with the second interior compartment; the second interior compartment being in fluidic communication with the first interior compartment and the first interior compartment being in fluidic communication with the first opening; the proximal end of the neck extension being connected to the sidewall of the first interior compartment at a first side; the neck extension extendable laterally in a direction away from the first side; the sidewall at the first interior compartment having a width perpendicular to a first longitudinal axis defined by a radial plane of the first opening when the bag is in undeflected configuration and a length along the first longitudinal axis; the neck extension having a width perpendicular to a second longitudinal axis defined by a radial plane of the second opening when in undeflected configuration and a length along the second longitudinal axis; the width of the neck extension being smaller than the width of the first interior compartment; and characterized by an external pocket on the sidewall sized and configured to contain the neck extension in a folded configuration.