A tissue-removing catheter comprising: a drive shaft having a length and a proximal end portion and a distal end portion spaced apart along the length, wherein the drive shaft is rotatable about a rotational axis; an ablation burr operatively connected to the drive shaft such that rotation of the drive shaft about the rotational axis imparts rotation of the ablation burr, the ablation burr having an abrasive outer surface configured for removing tissue from a body lumen, a handle adj acent the proximal end portion of the drive shaft; a carriage supported on the handle for movement with respect to the handle, the drive shaft being connected to the carriage such that the drive shaft moves with the carriage as the carriage moves with respect to the handle; and an alignment guide (270, 272) having a length and a fixed end portion and a movable end portion spaced apart along the length, the fixed end potion having a fixed position with respect to the handle, the movable end portion being connected to the carriage such that the movable end portion moves with the carriage with respect to the handle, the length of the alignment guide (270, 272) being extendable and retractable to allow the movable end portion to move relative to the fixed end portion; wherein the alignment guide (270, 272) is configured to engage a flexible elongate body (14, G) to align the flexible elongate body (14, G) with the carriage as the carriage moves relative to the housing; and wherein the flexible elongate body (14, G) comprises at least one of the drive shaft and a guidewire that extends through the housing; wherein the alignment guide (270, 272) comprises a telescoping assembly; wherein the telescoping assembly comprises a fixed end tube defining the fixed end portion of the alignment guide (270, 272) and a movable end tube defining the movable end portion of the alignment guide (270, 272), the movable end tube being slidably connected to the fixed end tube; characterized in that the telescoping assembly further comprises a middle telescoping subassembly having a first end portion that is slidably engaged with the fixed end tube and a second end portion that is slidably engaged with the movable end tube; wherein the middle telescoping subassembly includes at least a first tube and a second tube, the first tube being slidably received in the second tube; and wherein each of the first and second tubes (302, 300) has a length and comprises a stop, the stops being configured to engage one another as the alignment guide (270, 272) is retracted to prevent the first tube from radially overlapping the second tube along an entirety of the length of either of the first and second tubes (302, 300). a drive shaft having a length and a proximal end portion and a distal end portion spaced apart along the length, wherein the drive shaft is rotatable about a rotational axis; an ablation burr operatively connected to the drive shaft such that rotation of the drive shaft about the rotational axis imparts rotation of the ablation burr, the ablation burr having an abrasive outer surface configured for removing tissue from a body lumen, a handle adj acent the proximal end portion of the drive shaft; a carriage supported on the handle for movement with respect to the handle, the drive shaft being connected to the carriage such that the drive shaft moves with the carriage as the carriage moves with respect to the handle; and an alignment guide (270, 272) having a length and a fixed end portion and a movable end portion spaced apart along the length, the fixed end potion having a fixed position with respect to the handle, the movable end portion being connected to the carriage such that the movable end portion moves with the carriage with respect to the handle, the length of the alignment guide (270, 272) being extendable and retractable to allow the movable end portion to move relative to the fixed end portion; wherein the alignment guide (270, 272) is configured to engage a flexible elongate body (14, G) to align the flexible elongate body (14, G) with the carriage as the carriage moves relative to the housing; and wherein the flexible elongate body (14, G) comprises at least one of the drive shaft and a guidewire that extends through the housing; wherein the alignment guide (270, 272) comprises a telescoping assembly; wherein the telescoping assembly comprises a fixed end tube defining the fixed end portion of the alignment guide (270, 272) and a movable end tube defining the movable end portion of the alignment guide (270, 272), the movable end tube being slidably connected to the fixed end tube; characterized in that the telescoping assembly further comprises a middle telescoping subassembly having a first end portion that is slidably engaged with the fixed end tube and a second end portion that is slidably engaged with the movable end tube; wherein the middle telescoping subassembly includes at least a first tube and a second tube, the first tube being slidably received in the second tube; and wherein each of the first and second tubes (302, 300) has a length and comprises a stop, the stops being configured to engage one another as the alignment guide (270, 272) is retracted to prevent the first tube from radially overlapping the second tube along an entirety of the length of either of the first and second tubes (302, 300).